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 TECHNICAL SERVICES 
 COAST AND GEODETIC SURVEY 
 
 Rear Admiral 
 
 RoberhF.A. Shudds 
 
 Director 
 
 fy.S&epartment of Commerce 
 
 Charles Sawt/er, Secretary 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 LYRASIS Members and Sloan Foundation 
 
 http://archive.org/details/technicalserviceOOusco 
 
TECHNICAL SERVICES 
 
 U.S. COAST AND GEODETIC SURVEY 
 CONTENTS 
 
 GENERAL STATEMENT 3 
 
 COASTAL SURVEYS AND CHARTS 
 
 Original Surveys . 6 
 
 MARINE SERVICE - Plate IV 
 
 Nautical Charts 10 
 
 Related Nautical Publications . . 12 
 
 Coast Pilots 12 
 
 Distance Tables . 12 
 
 AERONAUTICAL SERVICE - Plate VI 
 
 Aeronautical Charts 15 
 
 TOPOGRAPHIC AND PLANIMETRIC MAPS 22 
 
 Topographic Maps 23 
 
 Planimetric Maps , 23 
 
 Photogrammetric Methods and Equipment 24 
 
 Aerial Photography 26 
 
 GEODETIC SERVICE - Plate XI 
 
 Geodetic Control Surveys 28 
 
 General Statement 28 
 
 Horizontal Control 28 
 
 Horizontal Control Data 30 
 
 Vertical Control 33 
 
 Leveling Data 33 
 
 Astronomy and Gravity . . 34 
 
 Latitude Observatories 34 
 
 TIDE AND CURRENT DATA 39 
 
 Tide and Current Tables . 40 
 
 Tidal Current Charts 40 
 
 Tidal Bench Marks 42 
 
 Temperature and Density of Sea Water 42 
 
 MAGNETIC DATA 44 
 
 SEISMOLOGICAL SERVICE - Plate XV 
 
 Seismological Data 48 
 
 U.S. DEPARTMENT OP COMMERCE 
 Charles Sawyer, Secretary 
 
 COAST AND GEODETIC SURVEY 
 Robert F. A. Studds, Director 
 
 July 1951 
 For sale by Coast and Geodetic Survey Price 75 cents 
 

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GENERAL STATEMENT 
 
 This publication describes the technical services of the 
 Coast and Geodetic Survey--a highly technical Bureau directly 
 aiding the United States Department of Commerce in carrying 
 out the mandate of Congress to promote, foster, and develop the 
 industry and commerce of the country. 
 
 The "Survey of the Coast" was organized on 1807, during 
 the administration of President Thomas Jefferson, but did not 
 begin operations until I8l6. Since then, it has functioned 
 without interruption, except for the periods 1818-32 and 1834- 
 36. Through the years the Bureau has been given the added re- 
 sponsibilities of the extension of geodetic control surveys 
 into the interior of the country and the compilation and pub- 
 lication of certain aeronautical charts. 
 
 Those engaged in travel, commerce, business, and engineer- 
 ing are provided an easy method of making full use of the data 
 collected by the Bureau for its charting and mapping activi- 
 ties. These engineering and scientific data, gathered through 
 field operations, are used essentially for water and air navi- 
 gation, mapping the country, developing natural resources, and 
 serving national defense. This information is becoming in- 
 creasingly valuable because of its collateral uses — engineer- 
 ing, industrial, and scientif ic--and its availability to 
 everyone. 
 
 The production of nautical and aeronautical charts is a 
 major function of the Survey. Sailing directions, tide tables, 
 current tables, and tidal current charts are published as sup- 
 plements to the nautical charts. Included in these activities 
 are the compilation and printing of aeronautical charts to 
 cover the United States, its Territories, and possessions as 
 required for civil aviation, and for military use where re- 
 quirements are parallel; and aeronautical charts to cover in- 
 ternational airways as required primarily by United States 
 civil aviation. 
 
 A basic responsibility of the Survey is the execution of 
 geodetic control surveys to provide control for maps; charts, 
 intermediate and local surveys; and various engineering pro- 
 jects, both public and private. Large-scale topographic and 
 planimetric maps of areas along the coasts of the country are 
 produced as by-products of the compilation of nautical charts. 
 Aerial photographs insure an adequate amount of reliable topo- 
 graphic detail on these charts. Tidal surveys are conducted 
 to reduce to a common level or datum plane the soundings taken 
 at different stages of the tide during hydrographic surveys. 
 Also essential in the preparation of nautical and aeronautical 
 charts are the magnetic surveys. Seismological studies and 
 
investigations, through the use of seismographs and the earth- 
 quake data which have been systematically collected, aid in 
 mapping earthquake areas and evaluating earthquake risks. 
 
 The data collected from other activities of the Bureau 
 are compiled and published in books and pamphlets, in addi- 
 tion to maps and charts. The Bureau likewise issues numerous 
 annual and special publications on the results of its opera- 
 tions and researches in triangulation, leveling, geomagnetism, 
 seismology, tidal phenomena, special tide and current studies 
 of particular harbors and rivers, and manuals covering its 
 various fields of work. 
 
 The products of the Survey grow in importance with the 
 increasing needs of our people and the spreading knowledge of 
 the many purposes for which they can be used to advantage. Its 
 labors must continue with unabated vigilance as long as the 
 waters flow, earthquakes occur, and changes are made by man and 
 nature. These very necessary services do not show themselves 
 directly by dollars-and-cents returns, but they reveal their 
 value in the untold wealth of added security to life and prop- 
 erty on land and sea. 
 
 Further information concerning the work of the Bureau 
 may be obtained upon request to the Director, U.S. Coast 
 and Geodetic Survey, Washington 25, D. C. 
 
COASTAL SURVEYS AND CHARTS 
 
 ORIGINAL SURVEYS 
 
 The Coast and Geodetic Survey since 1835 has made many 
 thousands of. topographic and hydrographic surveys along the 
 coasts of the United States, Alaska, and other possessions. 
 These surveys are the principal source of data used in the 
 construction and revision of nautical charts published by the 
 Bureau. They provide a comprehensive record of conditions 
 existing at the specific time a survey was made, whereas the 
 chart is generally a compilation of data secured at various 
 times. The topographic and hydrographic surveys are on much 
 larger scales than the nautical charts and, of course, show 
 considerably greater detail. They are independent of each 
 other: topographic surveys do not include soundings or other 
 hydrographic data; hydrographic surveys do not include details 
 of adjacent land areas. 
 
 Detailed topographic surveys used in conjunction with the 
 hydrographic surveys of the Bureau in the production and main- 
 tenance of nautical charts have been made for most of the 
 coastline of the United States and for extensive areas along 
 the coast of Alaska. Surveys between the years 1835 and 1935 
 were made by planetable methods. The recorded data include 
 detailed information on terrain characteristics adjacent to and 
 including the shoreline at the high-water line. Important 
 landmarks and mountain peaks which are visible at sea are the 
 only inland features usually included in the surveys. 
 
 Since 1927 aerial photographs have been used to compile 
 topographic surveys, and, in many cases, have been supplemented 
 by planetable surveys of the shoreline. The surveys made from 
 aerial photographs are published in the form of large-scale 
 planimetric maps described elsewhere in this publication. 
 
 Detailed hydrographic surveys have been made since 1835 
 for the entire coastline of the United States and most of 
 Alaska, as well as other insular possessions of the United 
 States. These surveys include the measurement of depths 
 (soundings); the determination of geographical positions of 
 such depths; and the location of shoals, banks, wrecks, aids 
 or obstructions to navigation, and other hydrographic features. 
 
 Some of these surveys are accomplished by means of the 
 wire drag. The wire drag is a method of hydrographic survey- 
 ing which makes possible the discovery of small obstructions 
 such as pinnacle rocks, boulders, ledges, et cetera. The wire 
 drag consists of a wire maintained at any desired depth which 
 is towed through the water by two launches. Lengths of drags 
 vary from 1,000 feet or less used in channel areas to 15,000 
 feet in open- water areas, which is about the limit that can be 
 handled with two towing launches. 
 
DEPARTMENT OF COMMERCE 
 COAST AND GEODETIC SURVEY 
 
 MARINE SERVICE 
 
 NAUTICAL CHARTS and related publications, essential for 
 
 the guidance and safety of navigation, are produced by the Coast 
 
 and Geodetic Survey for all coastal waters of the United States 
 
 and its possessions. 
 
 FIELD WORK 
 
 
 Hydrographic Surveys 
 
 
 Topographic (Coastal) Surveys 
 
 
 Tide and Current Surveys 
 
 
 
 Geodetic Control 
 
 
 Magnetic Surveys 
 
 
 Coast Pilot 
 
 
 BASIC MATERIAL- 
 
 PRODUCTION 
 -TWashington Office J- 
 
 OTHER INFORMATION 
 
 Aids to Navigation 
 (U.S. Coast Guard) 
 
 Channel Surveys 
 (U.S. Army Engineers) 
 
 iterior Topographic Surveys 
 (U.S. Geological Survey) 
 
 Local Information 
 (Bureau Field Stations) 
 
 MARINE PRODUCTS 
 
 Nautical Charts 
 
 Tide Tables 
 Current Tables 
 Current Charts 
 Coast Pilots 
 Basic Surveys 
 Special Magnetic Charts 
 
 DISTRIBUTION 
 
 Navy and Merchant Marine 
 
 Army and Coast Guard 
 
 Federal and State Agencies 
 
 Fishing Industry 
 
 Yachtsmen and Small Craft Operators 
 
 Foreign Marine Services 
 
 COLLATERAL USES 
 
 Construction of Port Facilities 
 
 Dredging and Harbor Developments 
 
 Beach Erosion and Sanitation Studies 
 
 Fishing Bank Locations 
 
 Waterfront Property Litigation Evidence 
 
 Submarine Geological Investigations 
 
 Oil Explorations 
 
 Submarine Cable and Pipeline Planning 
 
NAUTICAL CHARTS 
 
 One of the principal products of the Coast and Geodetic 
 Survey is the nautical chart, on which is shown all avail- 
 able information necessary for safe marine navigation. The 
 data included are of two kinds: vertical data described by 
 the depth and elevation figures and horizontal data locating 
 the features by latitude and longitude. In general, the data 
 shown on these charts are as follows: soundings; depth or 
 fathom curves; shoals; reefs; underwater dangers to navigation; 
 artificial aids to navigation; topographic and cultural fea- 
 tures; and shore installations, et cetera, adjacent to the 
 shore which are of aid to the mariner. These charts are litho- 
 graphed in color. Seldom are more than five colors used. 
 
 Nautical charts are produced primarily for the use of the 
 mariner, but they also serve the public interest in many other 
 ways as they are the most accurate source of detailed infor- 
 mation for the offshore areas and the coastal areas immedi- 
 ately adjacent to the shore. 
 
 All nautical charts must be revised constantly in order to 
 keep pace with the never-ending natural changes along our coasts 
 and the many man-made changes, such as dredging and harbor im- 
 provements, and changes in the aids to navigation. Upon re- 
 ceipt of this type of information, new editions or new prints 
 of the charts are prepared and published. Old editions are 
 canceled by new editions and should not be used. In addition 
 to these new editions and new prints, the charts are kept cur- 
 rent by hand corrections for critical changes reported to date 
 of issue. 
 
 Nautical charts vary In scale from 1:2,500 (Harbor Charts) 
 to 1:5,000,000 (Sailing Charts). These charts are of the fol- 
 lowing classifications: 
 
 Sailing Charts . -- Scales 1:600,000 and smaller. These 
 charts are intended primarily for use in fixing the mariner's 
 position as he approaches the coast from the open sea, or for 
 sailing between distant coastwise ports. The shoreline and 
 topography are generalized and only offshore soundings, prin- 
 cipal lights, outer buoys, and landmarks visible at a consider- 
 able distance are shown. 
 
 General Charts . -- Scale 1:100,000 to 1:600,000. These 
 charts are designed for offshore coastwise navigation outside 
 outlying banks and shoals. 
 
 Coast Charts . -- Scale 1:50,000 to 1:100,000. These charts 
 are designed for inshore coastwise navigation, for entering bays 
 
and harbors 01 considerable width, and for navigating large in- 
 land waterways. 
 
 Harbor Charts . -- Scales larger than 1:50,000. These 
 charts are planned for harbors, anchorage areas, and the smaller 
 waterways . 
 
 Intracoastal Waterway (inside route) Charts . -- Scale of 
 1:40,000. This is a special series of charts embracing the in- 
 side route in New Jersey; the route from Norfolk, Va., to Key 
 West, Fla., on the Atlantic coast; and from Key West, Fla., to 
 the Mexican boundary on the Gulf coast. These charts are de- 
 signed for harbors, anchorage areas, and the smaller waterways. 
 
 PUBLICATIONS OF GENERAL INTEREST 
 
 CATALOG OF NAUTICAL CHARTS AND RELATED PUBLICATIONS. 
 
 (U.S. Coast and Geodetic Survey) Serial 665. October 19^9- 
 49 P- Indexes for all nautical charts. (May be obtained only 
 from the Coast and Geodetic Survey, its field offices, or its 
 sales agents . ) 
 
 Other publications of a more general nature are listed in 
 "Related Nautical Publications" Section. 
 
RELATED NAUTICAL PUBLICATIONS 
 COAST PILOTS 
 
 The Coast Pilots published by the Coast and Geodetic Sur- 
 vey are primarily for navigational use; their purpose is to 
 furnish that information required by the navigator which cannot 
 be shown conveniently on nautical charts. Each Coast Pilot 
 covers a selected section of the coast and contains detailed 
 data relative to the coastline and harbors; port information; 
 sailing directions for coasting and entering harbors; and gen- 
 eral information as to weather conditions,, radio service, et 
 cetera. New editions are published about every 7 years. Sup- 
 plements, containing changes and new information, are published 
 annually and distributed free. The Coast Pilots are listed as 
 follows : 
 
 Atlantic Coast: 
 
 Section A, St. Croix River to Cape Cod, 1950 
 
 Section B, Cape Cod to Sandy Hook, 1950 
 
 Section C, Sandy Hook to Cape Henry, including 
 
 Delaware and Chesapeake Bays, 19^7 
 
 Section D, Cape Henry to Key West, 19^8 
 
 Gulf Coast: 
 
 Key West to the Rio Grande, 19^9 
 
 West Indies: 
 
 Puerto Rico and Virgin Islands, 19^9 
 
 Pacific Coast: 
 
 California, Oregon and Washington, 19^2 
 
 (1951 edition in 
 
 press) . 
 
 Alaska: 
 
 Part I. -Dixon Entrance to Yakutat Bay, 19^3 
 Part II. -Yakutat Bay to Arctic Ocean, 1947 
 
 Hawaiian Islands, 1950 
 
 DISTANCE TABLES 
 
 Tables of distances, in pamphlet form, have been compiled 
 for the purpose of giving in condensed and convenient form, 
 the distances between ports of the United States and its out- 
 lying Territories. Distances are given between some 10,000 
 ports along the shortest route marked by aids to navigation. 
 Also included is a time table for various distances at dif- 
 ferent speeds. 
 
DEPARTMENT OF COMMERCE 
 COAST AND GEODETIC SURVEY 
 
 AERONAUTICAL SERVICE 
 
 AERONAUTICAL CHARTS essential for the guidance and safety of air navigation 
 
 are produced by the Coast and Geodetic Survey for the U.S. and Alaska and for 
 
 special routes outside of the country. 
 
 FIELD WORK 
 
 Topographic (Coastal) Surveys 
 
 Airport Surveys 
 
 Magnetic Surveys 
 
 Flight Check 
 
 Geodetic Control 
 
 Obstruction Surveys 
 
 -BASIC MATERIAL 
 
 
 OTHER INFORMATION 
 
 
 Topographic Maps 
 (U.S. Geological Survey) 
 
 
 Topographic Maps 
 (U.S. Engineers) 
 
 
 Topographic Maps 
 (Soil Conservation) 
 
 
 Topographic Maps 
 (Forest Service) 
 
 
 
 Preliminary Topographic 
 (Army Air Force) 
 
 
 Aeronautical Information 
 (Civil Aeronautics Admn.) 
 
 
 Local Information 
 (Bureau Field Stations) 
 
 
 Miscellaneous Sources 
 
 PRODUCTION 
 — T Washington Office 1— 
 
 AERONAUTICAL PRODUCTS 
 
 Aeronautical Charts 
 Special Purpose Charts 
 
 SALES AGENTS 
 
 DISTRIBUTION 
 Washington Office 
 
 PRINCIPAL USERS 
 
 ARMY & NAVY 
 
 COMMERCIAL AIR CARRIERS 
 
 PRIVATE PILOTS 
 
 Aeronautical charts of foreign 
 areas produced by other agencies 
 distributed to civil aviation. 
 
 - [FIELD STATIONS 
 
AERONAUTICAL CHARTS 
 
 The Coast and Geodetic Survey compiles and prints aero- 
 nautical charts of the United States, its Territories, and 
 possessions as required for civil aviation, and for military 
 aviation where military needs are parallel to civil; and of 
 international airways as required for United States civil avia- 
 tion. Special emphasis is given to terrain features which 
 best serve the pilot in determining his course. Every effort 
 is made to include the outstanding landmarks in each locality. 
 Although they are compiled primarily for air navigation, the 
 charts also prove useful for many other purposes as the major 
 series provide contoured maps at a uniform scale. The base 
 chart is lithographed in color, and is overprinted with the 
 aeronautical data in magenta and offset blue. 
 
 The topographic and cultural features appearing on the 
 charts are compiled from the best information which is avail- 
 able. Relief on the major series is shown by contours, eleva- 
 tions, and a system of gradient tints employing shades of green 
 and brown. The cultural features include shoreline, drainage, 
 roads, railroads, cities and towns, and many prominent land- 
 marks. Certain items which should be included in a topographic 
 map are omitted in order not to obscure details of more im- 
 portance to the navigator, whereas other features are exagger- 
 ated because they are valuable as landmarks. 
 
 Aerodromes, low frequency radio aids, airways and control 
 areas, restricted airspace, high-tension lines, and other aids 
 or obstructions to air navigation are overprinted in magenta 
 on the base chart. 
 
 Very high frequency radio data (including Omni-direc- 
 tional ranges) are overprinted in offset blue on Sectional, 
 World Aeronautical, and Route Charts. 
 
 Complete coverage for the United States is available in 
 the Sectional Chart (1:500,000) and the World Aeronautical 
 Chart (1:1,000,000) series. Those Interested in charts of 
 these scales for uses other than aviation may obtain copies 
 of base charts without the aeronautical overprints. 
 
 Aeronautical charts vary in scale from 1:31,680 (airport 
 charts) to 1:5,000,000 (planning charts). These charts are 
 of the following classifications: 
 
 Sectional Charts . -- Scale 1:500,000. There are 87 charts 
 of this series covering the United States and 1 covering the 
 Hawaiian Islands. These charts are Intended primarily for 
 piloting—contact or landmark flying; therefore, effort is made 
 to include the outstanding landmarks in each locality. 
 
World Aeronautical Charts . -- Scale 1:1,000,000. There 
 are 43 charts of this series covering the United States and 
 adjacent areas of Canada and Mexico. Alaska is covered by 
 15 charts of the series. The reduced scale necessitates the 
 omission of some of the landmarks and topographic data of the 
 Sectional Charts; however, ample detail remains to provide 
 checks of the position determined by navigation methods. 
 
 Flight Charts . -- Scale 1:1,000,000. These are strip 
 charts covering areas approximately 100 miles on both sides of 
 principal air routes within the United States and Alaska, and 
 including connecting routes. There are 37 charts of routes 
 in the United States and 13 charts of routes in Alaska. 
 
 Local Charts . -- Scale 1:250,000. Twenty charts are pub- 
 lished to date of the series covering metropolitan areas: San 
 Juan, P.R.; Honolulu, T.H. ; and 18 cities in the United States. 
 These charts are designed to provide maximum landmark identifi- 
 cation of congested areas around major air terminals. 
 
 Instrument Approach and Landing Charts. -- Scale of Ap- 
 proach Charts 1:250,000; scale of Landing Charts 1:31,680. 
 These charts are designed primarily for use in an approach to 
 an airport under instrument- flight conditions, and they depict 
 let-down procedures based on the principal navigational aid 
 for the airport. The Landing Chart is printed on the back of 
 the corresponding Approach Chart . Each Approach Chart is 
 centered on the radio facility for the designated terminal. 
 There are over 400 charts of this series prepared for the prin- 
 cipal air terminals of the United States. 
 
 Instrument Landing System Charts . -- The 88 presently 
 published charts of this series cover principal United States 
 air terminals having ILS installations. The charts are de- 
 signed specifically for final instrument approaches of air- 
 craft using very high frequency instrument- landing equipment. 
 
 Radio Facility Charts . -- This series comprises 65 separ- 
 ate charts covering the United States and 14 covering Alaska. 
 The charts provide complete radio information to facilitate the 
 planning and execution of cross-country flights in the United 
 States. They are printed in green and black on standard size 
 paper, 8 by 10j inches. 
 
 Direction Finding Charts . -- Scale 1:2,000,000. These 
 charts are designed specifically to facilitate the plotting of 
 radio bearings. Magnetic compass roses are centered on the 
 charted radio stations. Six charts cover the entire United 
 States and three cover Alaska. 
 
Planning Charts . -- Scale 1:5.000,000. Chart AP-9 covers 
 the United States and chart 3069a covers Alaska. The charts 
 are designed for use in planning routes between distant points, 
 and show principal cities and towns, drainage, contours, and 
 gradient tints, overprinted with aeronautical data. 
 
 Aircraft Position Charts . -- Scale 1:5,000,000. There 
 are three charts of the series covering the North Atlantic, 
 Western Europe and Northwest Africa, and the Caribbean area. 
 The charts are designed for long-range air navigation opera- 
 tions over selected areas which require a special type of air 
 navigation chart suitable for overseas operations by U. S. 
 commercial air carriers. 
 
 Route Charts . -- Scale 1:2,000,000. There are nine charts 
 of this series: 7 cover the United States; and 2 cover air 
 routes from Chicago to Gander, Newfoundland; and from Shannon, 
 Ireland, to Rome, Italy. The charts employ the oblique Mer- 
 cator projection, which provides excellent properties for air 
 navigation over the selected routes. 
 
 Obstruction Plans . -- About 400 plans have been published 
 to date of principal United States airports. The series -will 
 include 550 plans when all now scheduled are completed. These 
 plans show the runways and all obstructions protruding above 
 a 40 to 1 glide angle from the end of the runways. 
 
 PUBLICATIONS OF GENERAL INTEREST 
 
 Other publications of a more general nature relating to 
 aeronautical charting and air navigation published by the 
 Coast and Geodetic Survey are: 
 
 TABLES FOR A P0LYC0NIC PROJECTION OF MAPS AND LENGTHS OF 
 TERRESTRIAL ARCS OF MERIDIAN AND PARALLELS BASED UPON 
 CLARKE'S REFERENCE SPHEROID OF 1866. Special Pub. 5- 
 Sixth edition 1935- 1 Illus. 
 
 GENERAL THEORY OF POLYCONIC PROJECTIONS. Oscar S .' Adams. 
 Special Pub. 57, Serial 110. 1934. 174 P- 49 illus. 
 
 ELEMENTS OF MAP PROJECTION WITH APPLICATIONS TO MAPS AND 
 CHART CONSTRUCTION. Charles H. Deetz and Oscar S. Adams. 
 Special Pub. 68. Fifth edition, revised 1944. 226 p. 
 89 illus. 15 plates. 
 
 TABLES FOR ALBERS PROJECTION. Oscar S. Adams. Special 
 Pub. 130. Serial 378. 1927- 26 p. 
 
CONFORMAL PROJECTION OP THE SPHERE WITHIN A SQUARE. Oscar 
 S. Adams. Special Pub. 153- 15 p. 4 illus. 
 
 CARTOGRAPHY. Charles H. Deetz. Special Pub. 205- 19^3- 
 91 p. 30 illus. 
 
 LAMBERT CONFORMAL CONIC PROJECTION TABLES. Standard 
 parallels, 7° and 20°, 8l p.; 17° and 33°, l4l p.j 33° 
 and 45°, 83 p.; 45° and 58 , 140 p.; 55° and 65 , 158 p.j 
 30° and 75°, 3 P- Volumes I and II--Tables with standard 
 parallels for each 4° band of latitude from the equator 
 to 80° latitude - computed with values for both "a" and 
 "b" and "x" and "y" methods of construction. 
 
 OBLIQUE MERCATOR PROJECTION TABLES. In 19 bands pro- 
 viding world-wide coverage, each band has an effective 
 width of 16 degrees of a great circle. This publication 
 contains 187 pages of tables, explanatory text, mathe- 
 matical formulas for deriving the tables, and a nomograph. 
 
 DISTANCE TABLES (Airline) 
 
 AIRLINE DISTANCES. C. A. Whitten. Special Pub. 238. 
 245 p. An extensive table of more than 120,000 airline 
 distances between 492 cities in the United States which 
 are authorized points on routes of domestic air carriers. 
 
TOPOGRAPHIC AND PLANIMETRIC MAPS 
 
 The Coast and Geodetic Survey produces large-scale topo- 
 graphic and planimetric maps of the coastline and adjacent land 
 areas as essential by-products in the compilation and revision 
 of nautical charts. The maps are produced on scales of 1:10,000 
 and 1:20,000; a few, for special purposes, are on a scale of 
 1:5*000 or larger. Annual production averages 50 large-scale 
 topographic maps (1,800 square miles), 45 planimetric maps 
 (1,500 square miles), and 35 shoreline survey sheets (400 
 linear miles) . 
 
 These maps are compiled from field-checked aerial photo- 
 graphs, which in many cases have been supplemented by plane- 
 table surveys of the shoreline. Experience indicates that a 
 basic aerial photographic survey of the coast and adjacent land 
 areas can cost less than a ground survey limited to revision 
 along the shoreline only. Aerial photographs insure an ade- 
 quate amount of reliable topographic detail for nautical charts, 
 and also furnish basic information to engineers, county sur- 
 veyors, and others interested in the development of coastal 
 areas. They present a picture of conditions and advantages so 
 complete and reliable as to be of benefit in promoting the 
 growth to be expected from the immense investments for inside 
 waterways and harbor improvements. Requests often come from 
 commercial companies for copies of these maps before the 
 originals are received for reproduction. 
 
 All maps of this series are based on triangulation or 
 traverse control. Recoverable objects are generally distributed 
 either by marking stations or by selecting natural objects at 
 intervals close enough to furnish control points at a maximum 
 distance of 1 mile apart. Permanent survey marks of the Survey 
 and other Federal agencies and local organizations are shown. 
 These maps are on polyconic projections; some show state plane 
 coordinates, and In the future all will. 
 
 Types of maps produced by the Survey are: (l) Topographic 
 maps, which include contours, of the lands adjacent to the 
 navigable coastal waters of the United States. They provide 
 complete topographic data for the compilation of nautical 
 charts. (2) Planimetric maps complete for all shore and in- 
 shore details, except contours. (3) Shoreline surveys for 
 areas requiring revision of the shoreline where existing plani- 
 metric or topographic maps are adequate for interior details. 
 Shoreline surveys are registered in the permanent topographic 
 surveys file but are not reproduced for general distribution. 
 (4) Airport obstruction plans for all Important airports of the 
 United States, which are special-purpose charts, show runway 
 patterns and other essential airport information. They are pro- 
 duced specifically tc show the positions and elevations of all 
 obstructions within 3 miles of runway termini. Elevations are 
 
determined by ground surveys; obstructions are located by field 
 surveys, usually with the aid of aerial photographs. 
 
 Topographic Maps . -- Compiled on a 7^-minute quadrangle 
 basis for areas where existing maps do not contain adequate data 
 for nautical chart purposes, topographic maps cover land fea- 
 tures adjacent to the shoreline and other land features essen- 
 tial to nautical charts as aids in alongshore navigation. With 
 the advent of radar navigation, landforms are becoming increas- 
 ingly important to the navigator. The mapped area usually con- 
 sists of a strip a few miles wide along the coastline, extend- 
 ing along the entire seacoast, around bays, and up rivers to the 
 head of navigation. In special cases, the maps Include inland 
 areas to meet specific requirements. 
 
 The quadrangles are usually compiled from aerial photo- 
 graphs by stereoscopic mapping instruments, or occasionally they 
 may be derived by a combination of graphic compilation from 
 aerial photographs and planetable surveys. After the manu- 
 scripts have been completed by the Coast and Geodetic Survey, 
 including field-edit and review, they are turned over to the 
 U.S. Geological Survey for publication as basic components of 
 the standard topographic series of the United States. 
 
 Planimetric Maps . — The Coast and Geodetic Survey has pub- 
 lished more than 1000 large-scale planimetric maps covering ex- 
 tensive areas along the coasts of the country. Their compila- 
 tion from aerial photographs has expanded to include surveys of 
 the coastal regions and intracoastal waterways of most of the 
 Atlantic coast and extensive areas of the Gulf and Pacific 
 coasts . 
 
 Planimetric maps serve admirably as base maps for coordina- 
 ting and compiling all the surveys of a locality. There is a 
 great need, particularly among county engineers, for an accurate 
 base map coordinated with the geodetic datum at a scale large 
 enough to show the details of developments on which other survey 
 and map data can be plotted without risk of accumulated error. 
 The planimetric maps show all the important f eatures--except 
 contours- -which are distinguishable on the aerial photographs in 
 their true relation to geodetic control. Features include 
 shoreline detail; drainage; and cultural details such as towns, 
 buildings, roads, railroads, field boundaries, and landmarks. 
 The cadastral surveys of a region are frequently connected to 
 the details so that they can be plotted on the planimetric maps 
 with a minimum of expense for resurveys. Special construction 
 surveys may also be plotted with equal facility; more intelli- 
 gent development may be expected of the localities where surveys 
 have been coordinated and mapped in this way. 
 
 Planimetric maps do not contain hydrographic information. 
 They are printed in one color (black), without scale reduction. 
 The maps vary in size but are generally about 26 by 44 inches, 
 
and are distributed at 75 cents each by the Coast and Geodetic 
 Survey. Indexes showing the areas covered, with each map iden- 
 tified for ordering, may be obtained upon request. 
 
 Planimetric and shoreline surveys of areas of low relief 
 are mapped from nine- lens photographs by radial plotting and 
 graphic compilation methods. The control ordinarily consists 
 of existing first- and second-order triangulation. 
 
 Phot ogramme trie Methods and Equipment . -- Aviation has 
 simplified the production of aerial photographs for a given 
 area. This development paved the way for photogrammetric 
 methods of mapping to replace in large part ground planetable 
 surveying which was formerly used almost exclusively by the 
 Survey. The more economicial and expeditious method of photo- 
 grammetry was first used in surveying the Alaska-Canada boundary 
 in the 1890 ' s . At that time photographs were taken from the 
 ground at' points of known position and used In lieu of plane- 
 table observations to determine the positions of minor points 
 of detail. Although this method of terrestrial photogrammetry 
 was used with considerable success, it was not generally 
 adopted, and was not used again until 1918, when some aerial 
 photographs became available for experimental surveys. Photo- 
 grammetry, Which is more complete in coverage and less tedious 
 in application, soon demonstrated superiority over ground plane- 
 table surveying, and since 1928 has developed rapidly as the 
 method now used for nearly all of the Bureau's topographic 
 surveys . 
 
 In producing maps from single-lens photographs, consider- 
 able expensive ground control was required to combine a large 
 number of photographs into an accurate plot. To overcome these 
 difficulties, personnel of the Survey designed a nine-lens 
 aerial camera and associated equipment. The camera has nine 
 lenses of 8^-inch focal length and produces at each exposure 
 nine separate images on one piece of film. The images are 
 transformed and combined into a composite photograph approxi- 
 mately 35 inches square, affording an excellent detailed view 
 of the ground. At an altitude of 7,000 feet, an area of 32 
 square miles is covered. This coverage increases to over 300 
 square miles at an altitude of 22,000 feet. Ground control 
 necessary for aerial photographic surveys is thereby reduced, 
 with a corresponding reduction in the cost of mapping from 
 photographs. This is especially true where transportation is 
 difficult and costly. 
 
 Stereoscopic plotting instruments have been designed espe- 
 cially for use with the nine-lens prints. Stereoscopic pairs 
 of rectified aluminum-mounted photographs are used on these 
 plotting machines, known as Reading plotters, named after their 
 designer, Capt. 0. S. Reading, Coast and Geodetic Survey. A 
 
visual relief model is obtained by the simultaneous examination 
 of an overlapping pair of photographs and, by means of automatic 
 parallax-analyzing mechanisms and scale correctors, heights and 
 contours are accurately measured and traced. 
 
 Topographic maps are compiled from single- lens photographs 
 by a Zeiss stereoplanigraph, three Bausch and Lomb multiplex 
 units, and two Kelsh plotters. The s t er e op lani graph, used with 
 single-lens photographs for horizontal and vertical bridging or 
 aerial triangulation between ground control stations, is more 
 accurate than other instruments of the Survey, and it is ex- 
 tremely flexible with regard to scale of compilation. In some 
 applications, data .obtained with the stereoplanigraph are used 
 as control for adjusting the multiplex and the Kelsh plotters, 
 with which the final detailing and contouring are done. 
 
 Aerial Photography . — The Bureau maintains its own person- 
 nel and equipment for taking and processing aerial photographs 
 used for chart correction, topographic and planimetric mapping, 
 and airport obstruction plans. The equipment includes three 
 single-lens aerial cameras, a nine-lens camera, and a well- 
 appointed photographic laboratory. The photographic crew usu- 
 ally operates in Alaska during the summer months and in the 
 United States the remainder of the year. The extent of photo- 
 graphic coverage is shown on an accompanying map. (Contact 
 prints and enlargements of single- lens aerial photographs may 
 be purchased. ) 
 
 Aerial photographs are taken from a B-17 aircraft, equipped 
 with a plexiglass nose for the navigator. This sturdy long- 
 range plane, especially suitable for the Survey's photography, 
 particularly in sparsely settled Alaska, is equipped with two 
 camera mounts, one for the nine- lens camera and one for the 
 single-lens cameras. It is owned and operated by the U.S. Coast 
 Guard, but the navigator and photographer are employees of the 
 Survey. 
 
 Graphic compilation of planimetric maps and shoreline sur- 
 veys from single- lens enlargements and nine- lens photographs 
 comprises a relatively large proportion of the work of the 
 Division of Phot ogramme try. Radial line plots are very care- 
 fully made with transparent vinylite templets, which are cor- 
 rected graphically for paper shrinkage during their preparation. 
 
 PUBLICATIONS OF GENERAL INTEREST 
 
 Publications by the Coast and Geodetic Survey relating to 
 topographic surveys are listed as follows: 
 
TOPOGRAPHIC MANUAL. 0. W. Swainson. Special Pub. 144. 
 1928. 125 p. 40 illus. 
 
 TOPOGRAPHIC MANUAL. Part II. L. W. Swanson. Special Pub. 
 249. 1949. 570 p. 192 illus. A statement of the Bur- 
 eau's general requirements for photogrammetry and topo- 
 graphic surveying. Part I, to be published at a later 
 date, will contain detailed instructions for field topo- 
 graphic surveys, including planetable surveys, without 
 using aerial photographs, and phot ogramme trie field surveys 
 made for the compilation of maps from aerial photographs. 
 When published, Part I will supersede Special Pub. 144. 
 
GEODETIC CONTROL SURVEYS 
 
 GENERAL STATEMENT 
 
 The surveying and mapping of large areas require the con- 
 sideration of the geoid--the curvature of the sea level surface 
 of the earth. Basic surveys which take into account the size 
 and shape of the earth are called geodetic surveys. 
 
 The geodetic work of the Coast and Geodetic Survey con- 
 sists of several types of surveying operations, which require 
 the highest degree of accuracy. The resulting data are used as 
 the basis or control for maps, charts, intermediate and local 
 surveys, and for various engineering projects, both public and 
 private . 
 
 The operations include the determination of latitudes and 
 longitudes by triangulation and traverse; the determination of 
 elevations by leveling; astronomic observations for latitude, 
 longitude, and azimuth in conjunction with triangulation and 
 traverse; and gravity observations for determination of the 
 figure of the earth. 
 
 HORIZONTAL CONTROL 
 
 Triangulation is a very efficient method for making surveys 
 over extensive areas. It avoids the tedious time-consuming, 
 expensive operation of measuring the lengths of all lines that 
 enter into a survey. It consists of a system of connected 
 triangles with all angles carefully observed, but with only an 
 occasional length actually measured on the ground. Each meas- 
 ured length is known as a base. An intricate network of arcs 
 or chains of triangulation has been extended over the United 
 States. The areas between the arcs are being filled with a 
 spider-web effect to locate points at closer intervals. These 
 points, designated as triangulation stations, are located by 
 surveys of first-, second-, and third-order accuracy, and the 
 geographic positions are adjusted on the North American 1927 
 datum. 
 
 The United States has been covered in large part by a net- 
 work of triangulation (see diagram). The geographic positions 
 have been determined for approximately 150,000 stations in the 
 United States and Alaska. They consist of marked or monument ed 
 points and prominent objects, such as water tanks, church 
 spires, cupolas, chimneys, et cetera. Engineers and surveyors 
 may begin and end local surveys on these stations, and by using 
 plane coordinates in their computations employ only the usual 
 formulas and tables of plane surveying. Plane coordinates are 
 computed on the state systems for all stations in the United 
 States_ for which positions have been adjusted on the North 
 American 1927 datum. 
 
DEPARTMENT OF COMMERCE 
 COAST AND GEODETIC SURVEY 
 
 GEODETIC SERVICE 
 
 GEOGRAPHIC POSITIONS (latitude and longitude of monumented stations), 
 elevations of bench marks, and related data, essential for charting, 
 mapping, and other engineering projects, are provided by the Coast 
 and Geodetic Survey throughout the United States and its possessions. 
 
 FIELD WORK 
 
 
 Triangulation 
 
 
 Leveling 
 
 
 
 Gravimetric Surveys 
 
 
 Astronomic Surveys 
 
 
 BASIC MATERIAL 
 
 PRODUCTION 
 —£ Washington Office^— 
 
 
 OTHER INFORMATION 
 
 
 Local Control Surveys 
 (Government Mapping Agencies) 
 
 
 
 Condition of Station and 
 
 Bench Marks 
 (Miscellaneous Sources) 
 
 GEODETIC DATA 
 
 Geographic Positions 
 
 Plane Coordinates 
 
 Elevations 
 
 Gravity Data 
 
 Astronomic Data 
 
 isc. Mathematical Tables 
 
 1 
 
 DISTRIBUTION 
 
 X 
 
 FIELD STATIONS 
 
 PRINCIPAL USERS 
 
 Bureau Field Parties 
 
 (Charting Surveys) 
 
 Government Mapping Agencies 
 
 (Topographic Mapping) 
 
 U.S. Engineers-Reclamation Service 
 
 (Public Works Projects) 
 
 Oil Companies 
 
 (Geophysical Prospecting for Oil) 
 
 State-Municipal and Private Engineers 
 
 (Highway and Railroad Construction) 
 
 (State Conservation and Other Projects) 
 
 (Urban Development Projects) 
 
 (Cadastral and Boundary Surveys) 
 
Marked stations normally consist of bronze triangulation 
 station disks set in concrete, bedrock, or existing permanent 
 structures. Each station is usually referenced by two similar 
 marks designated as reference marks located nearby. Usually 
 an azimuth mark, similarly marked and visible from the station, 
 is located at least 1/4 mile distant to furnish convenient 
 azimuth control for local surveys. Only the azimuth from the 
 station to this mark is observed; the distance is not determined 
 and the azimuth is not observed from other stations. 
 
 Generally the elevations of triangulation stations and the 
 geographic positions or plane coordinates of bench marks are 
 not determined. Triangulation stations are necessarily located 
 on high points so that there may be visibility between stations, 
 whereas lines of leveling follow railroads and highways where 
 there are no sharp changes of elevation. Therefore, it is only 
 in rare instances that spirit-level elevations of triangulation 
 stations or the positions of bench marks are determined. In 
 high, mountainous country, elevations of triangulation stations 
 are often determined by vertical-angle observations. Such 
 elevations may be in error by several feet because of the un- 
 known refractive effect of the atmosphere. Various marked 
 stations, prominent features, and structures along the coast 
 not determined by triangulation or traverse have been located 
 by planetable or air-photographic methods. 
 
 HORIZONTAL CONTROL DATA 
 
 The data for triangulation and traverse stations estab- 
 lished by the Survey are available for the use of engineers 
 and surveyors. The initial computations and adjustments of 
 observations are made with geodetic factors producing latitudes, 
 longitudes, geodetic azimuths, and lengths. These computa- 
 tions are rather formidable for the local engineer who may 
 have had little opportunity to become experienced in the use 
 of the special formulas and tables required. This difficulty 
 has been almost entirely overcome by the introduction of state 
 plane coordinate systems. The data for triangulation stations 
 of the Bureau now include the vV x "and Vp lane rectangular co- 
 ordinates of each station as well as the latitude and longitude. 
 In connecting to these stations the local engineer may consider 
 only the plane coordinates and compute his surveys on the 
 simple rectangular system. His surveys will be coordinated 
 with the national net just as effectively as if he had used 
 the more difficult geodetic method of computation. Further- 
 more, he may later derive the latitudes and longitudes of a 
 few important points of his survey without too much difficulty 
 by converting from one system to the other. For this purpose, 
 plane coordinate projection tables for each state may be ob- 
 tained from the Bureau. 
 
The geodetic data are In lithoprint form and are available 
 for distribution without cost. Included are the latitudes, 
 longitudes, and plane coordinates of the stations, the geodetic 
 lengths and azimuths of the lines between contiguous stations, 
 and the detailed descriptions of their locations. The geodetic 
 azimuths or directions of the lines should not be confused with 
 the plane coordinate directions which may differ considerably. 
 The convergence of the meridians is considered in deriving the 
 geodetic azimuths, whereas the plane or grid azimuths are refer- 
 red to one central meridian. In order to make data available 
 in the shortest possible time, and in flexible form so that 
 additions and necessary corrections can be made, a loose-leaf 
 system is used. 
 
 Descriptions . -- Station descriptions are lithoprinted 
 by arcs and areas as the work is done, and are available by 
 individual pages or by groups of pages assembled by projects 
 which are arbitrarily numbered. The station descriptions are 
 arranged geographically along the arcs or by counties for area 
 coverage . 
 
 Geographic Positions . -- The latitudes and longitudes of 
 stations and lengths and azimuths of observed lines between 
 them are lithoprinted, when the adjusted data become available, 
 by arcs or areas and the pages are assembled in volumes by 
 states. It should be noted that these data are not necessarily 
 assembled in the same area coverage as the descriptions. 
 
 Plane Coordinates . -- The *x' and V" coordinates are litho- 
 printed for all stations in the United States which have been 
 adjusted on the North American 1927 datum. Plane azimuths to 
 azimuth marks and, in the more recent lists, the difference 
 between the plane and geodetic azimuths are included. Plane 
 coordinates are computed from the geographic positions and are 
 generally listed in the same sequence within states or zones. 
 The plane-coordinate data are not necessarily assembled in the 
 same area coverage as the descriptions. 
 
 Triangulation Diagrams and Indexes. -- Triangulation and 
 traverse stations are plotted on state base maps of convenient 
 scale as graphic indexes of the location of the stations and 
 the lines observed in the field work. Indexes of triangulation 
 data are available for each state giving volume and page numbers 
 for geographic positions, and plane coordinates and descrip- 
 tions, respectively. 
 
VERTICAL CONTROL 
 
 Leveling, the operation of determining the difference of 
 elevation between any two points on the surface of the earth, 
 has been extensively carried on in the United States by the 
 Coast and Geodetic Survey. Elevations resulting from leveling 
 may be computed relative to some arbitrary or natural level 
 surface called a datum. The datum used by the Survey is the 
 mean level of the sea, and the elevations are referred to as 
 being based on the "Sea Level Datum of 1929" as the primary 
 adjustment of the first-order level net was computed at that 
 time . 
 
 Most of the level lines run by the Survey follow the routes 
 of highway and railroad systems for economic reasons. To per- 
 petuate the leveling, brass-disk bench marks are established 
 along the route of the lines at intervals of 1 to 3 miles, 
 except in towns and cities, where several are usually placed. 
 On each bench-mark disk is an appropriate legend and the letter 
 and number forming the designation. They are set in the top of 
 specially made stone or concrete posts, in the walls of sub- 
 stantial buildings, in any solid masonry structure, in outcrops 
 of rock, et cetera. The elevations of a number of unmarked 
 points, such as the intersection of highways and the top of the 
 rail in front of a railroad station, are also determined. 
 
 The Coast and Geodetic Survey level lines are generally 
 of first- and second-order accuracy. Only a very small 
 amount of third-order leveling has been run by this organiza- 
 tion. The most accurate method of leveling is first-order. An 
 idea of the accuracy attained in first-order leveling is given 
 by the fact that on an average a circuit 100 miles in length 
 closes with an error of only slightly over 1 inch. 
 
 The elevations of more than 275,000 bench marks in the 
 United States have been determined by the Coast and Geodetic 
 Survey on approximately 380,000 miles of first- and second- 
 order leveling. 
 
 LEVELING DATA 
 
 The Coast and Geodetic Survey's data for leveling are 
 available in lithoprint form. These include descriptions and 
 locations of bench marks and elevations above mean sea level. 
 The data are printed for lines of leveling. Each line has a 
 distinctive number, which is shown on state maps of convenient 
 size. The index maps and lithoprinted data concerning leveling 
 are available from the Coast and Geodetic Survey upon request. 
 
ASTRONOMY AND GRAVITY 
 
 A continuous program of field astronomic observations is 
 maintained. These observations are used to control orientation 
 of triangulation networks,, and, in conjunction with gravimetric 
 data, to provide increasingly more information on the size and 
 shape of the earth. Approximately one thousand astronomic 
 stations have been established under this program. 
 
 The gravity activities of the Survey include pendulum 
 observations at more or less regular intervals throughout the 
 country to provide a system of gravity control, and, in recent 
 years, the use of gravity meters to obtain more detailed gravity 
 coverage. Gravity anomalies are computed according to various 
 hypotheses, and the resulting data are used in studies of the 
 figure of the earth. These data are also widely used by geo- 
 physicists and geologists in interpretations of density distri- 
 butions in the earth's crust'. 
 
 LATITUDE OBSERVATORIES 
 
 As the earth rotates, the axis of rotation points very 
 nearly but not exactly to a fixed point in the heavens. Imagine 
 a line through the center of the earth and the celestial North 
 Pole, then this line would describe an Irregular curve of a 
 14-month period around the mean North Pole. The largest dis- 
 tance between this curve and the mean Pole is of the order of 
 0'.'3 to 0'.'4, or 30 to 40 feet. 
 
 All astronomical observations are directly affected by 
 this variation of the Pole. In order to correct astronomical 
 observations for the variation of the Pole, a continuous record 
 of its wandering or variation must be available. No theory has 
 been developed by which the variation of the Pole can be predic- 
 ted to any degree of accuracy. 
 
 In 1o99j five international latitude observatories were 
 established for the purpose of keeping a continuous account of 
 the variation of the Pole. All observatories are on the same 
 parallel of North latitude, = 39° 0812. This assures the use 
 of the same set of stars by each station, thus eliminating any 
 errors in positions of the star places, and also insuring that 
 the conditions for observing are almost identical for the same 
 set of stars at all stations. The five observatories are loca- 
 ted at Ukiah, Calif.; Gaithersburg, Md.; Carlo Forte, Italy; 
 Kitab, Russia; and Misuzawa, Japan. The first two, in the 
 United States, are maintained by the Coast and Geodetic Survey. 
 
PUBLICATIONS OP GENERAL INTEREST 
 
 Publications by the Coast and Geodetic Survey covering the 
 methods by which triangulation and leveling are carried on, or 
 special subjects connected with either methods or results, are: 
 
 FORMULAS AND TABLES FOR THE COMPUTATION OF GEODETIC 
 POSITIONS. Special Pub. 8. Seventh edition. The method of 
 computing geodetic positions by the use of logarithms is ex- 
 plained and the tables used in the computations are given. 
 
 APPLICATION OF THE THEORY OF LEAST SQUARES TO THE ADJUST- 
 MENT OF TRIANGULATION. Special Pub. 28. The purpose of this 
 publication is to illustrate the application of the method of 
 least squares to the problems arising in the adjustment of 
 triangulation. 
 
 INSTRUCTIONS TO LIGHTKEEPERS ON FIRST-ORDER TRIANGULATION. 
 Special Pub. 65. This manual describes the lightkeeper ' s duties 
 in tending signal lights and describes his instruments, their 
 use and care. 
 
 MANUAL OF FIRST-ORDER TRAVERSE. Special Pub. 137- This 
 volume summarizes the methods used in executing first-order 
 traverse. It contains detailed instructions for the various 
 operations in the conduct of field work, describes the records 
 and computations to be made In the field; explains in detail 
 the office computation, including the least squares adjustment; 
 and contains a number of tables needed in making the computa- 
 tions . 
 
 MANUAL OF TRIANGULATION COMPUTATION AND ADJUSTMENT. Spe- 
 cial Pub. 138. The purpose of this publication is to explain 
 the methods used by the Coast and Geodetic Survey in the office 
 computation and adjustment of triangulation. 
 
 MANUAL OF SECOND- AND THIRD-ORDER TRIANGULATION AND TRA- 
 VERSE. Special Pub. 145- This publication contains a des- 
 cription of the specifications and criteria for second- and 
 third-order triangulation, traverse, and base measurement, with 
 detailed instructions for field and office operations and speci- 
 mens of field records and office computations. 
 
 BILBY STEEL TOWER FOR TRIANGULATION. Special Pub. 158. 
 (Rev. 19^0, Ed.). The design and use of the portable steel 
 tower for triangulation work was one of the foremost advances 
 made in recent years by the Coast and Geodetic Survey in its 
 endeavor to reduce the cost of its work while maintaining or 
 improving its accuracy. The Bilby tower is much less expensive 
 than the wooden tower formerly used and can be promptly erected 
 to the height needed, and readily dismantled and moved by truck 
 
to the next station. This publication contains not only illus- 
 trations, drawings , and specifications for the construction of 
 these steel towers but also comprehensive instructions for 
 organizing a field building party, including personnel and out- 
 fit. It describes the method used for marking stations, and 
 other operations required in cooperating with the observing 
 party. 
 
 MANUAL OF PLANE COORDINATE COMPUTATION. Special Pub. 193- 
 This is a description of the two types of conformal projections 
 that have been used as bases for the state systems of plane 
 coordinates . 
 
 MANUAL OF TRAVERSE COMPUTATION ON THE LAMBERT GRID. Spe- 
 cial Pub. 194. A supplement to Special Pub. 193; this manual 
 contains a more complete account of the system of plane coordi- 
 nates based on the Lambert projection. 
 
 MANUAL OF TRAVERSE COMPUTATION ON THE TRANSVERSE MERCATOR 
 GRID. Special Pub. 195* This is a companion volume to Special 
 Pub. 194 and serves the same purpose for the transverse Mercator 
 projection. 
 
 MANUAL OF RECONNAISSANCE FOR TRIANGULATION. Special Pub. 
 225. Reconnaissance is essentially the design of triangulation. 
 It includes the selection of sites for stations, the testing 
 of lines for visibility, the determination of required signal 
 heights, and the collection of local information which will 
 expedite the work of the building and observing parties. In- 
 structions for this important operation in triangulation surveys 
 are included in this manual. 
 
 CONTROL LEVELING. Special Pub. 226. Describes in non- 
 technical language the precise leveling operations of the Coast 
 and Geodetic Survey. Includes descriptions of instruments, 
 methods of field operations and office adjustments, history of 
 the level net, and other special information on leveling. 
 
 HORIZONTAL CONTROL DATA. Special Pub. 227. Gives essen- 
 tial facts about the Survey's horizontal control method in 
 simple non-technical language. Explains horizontal control 
 data and their uses. 
 
 NATURAL SINES AND COSINES TO EIGHT DECIMAL PLACES. Spe- 
 cial Pub. 231. This eight-place table with an interval of one 
 second is useful in computing geographic positions by calculat- 
 ing machine. 
 
 THE STATE COORDINATE SYSTEMS (A Manual for Surveyors.) 
 Special Pub. 235- The primary purpose of this manual Is to 
 present the simplification of the use of the state plane 
 
coordinate systems by engineers and surveyors who may wish to 
 connect their surveys to the national control net without the 
 difficulty of making geodetic computations. 
 
 MANUAL OP GEODETIC ASTRONOMY. Special Pub. 237. This is 
 a manual for field and office use, describing the methods used 
 in the observation and computation of astronomical determina- 
 tions connected with geodetic surveys. It deals especially with 
 the use of the Bamberg broken-telescope transit instrument for 
 determining latitude and longitude, and also for determining 
 azimuth in high latitudes. 
 
 MANUAL OP GEODETIC LEVELING. Special Pub. 239. This 
 manual contains the general instructions and procedure for 
 geodetic leveling as practiced by the Coast and Geodetic Sur- 
 vey. 
 
 MANUAL OF LEVELING COMPUTATION AND ADJUSTMENT. Special 
 Pub. 24-0. This is strictly an office manual describing in 
 detail the methods of computing and adjusting first- and second- 
 order leveling. 
 
 NATURAL TABLES FOR THE COMPUTATION OP GEODETIC POSITIONS. 
 Special Pub. 24l. The method of computing geodetic positions 
 by the use of natural functions is explained and tables used 
 in the computations are given. 
 
 DEFINITIONS OF TERMS USED IN GEODETIC AND OTHER SURVEYS. 
 Special Pub. 242. Gives authoritative definitions, principally 
 of geodetic survey terms. 
 
 PENDULUM GRAVITY DATA IN THE UNITED STATES. Special Pub. 
 244. This publication contains the descriptions, positions, 
 elevations, observed values of gravity, and gravity anomalies 
 for all pendulum gravity stations established in the United 
 States between 1891 and 1949. Included is a short discussion 
 of the gravity ties between the gravity base stations in 
 Washington, D.C., and the absolute-gravity station in Potsdam, 
 Germany . 
 
 SINES, COSINES, AND TANGENTS; TEN DECIMAL PLACES, WITH TEN- 
 SECOND INTERVAL; 0° - 6°. Special Pub. 246. This trigonometric 
 table was compiled primarily for use in computing state plane 
 coordinates on the Lambert projection. 
 
TIDE AND CURRENT DATA 
 
 The tidal work of the Bureau had its origin in the neces- 
 sity for reducing to a common level, or datum plane, soundings 
 taken at different stages of the tide during hydrographic sur- 
 veys . At the present time this work has developed in the 
 following fields: The determination of mean sea level and 
 other tidal datum planes for surveying and engineering purposes 
 and the establishment of a system of tidal bench marks to which 
 these planes are referred; the prediction of tides and currents 
 and the publication of annual tide and current tables which 
 include these predictions, together with other tide and current 
 data; the publication of current charts for harbors and other 
 waterways, which show the velocity and direction of the current 
 at different hours; the publication of tide and current obser- 
 vational data, in general, as a matter of record, and to afford 
 material for a study of various problems involving the tidal 
 phenomena; the observation of the temperature and density of 
 sea water at tide stations; and the study of seiche, seismic 
 sea waves, storm tides, and other oceanographic phenomena which 
 either relate to tides or are recorded incident to obtaining 
 the tide record. 
 
 The primary object of the current work of the Bureau is 
 the determination of navigational data, such as the velocity 
 and direction of the currents; the determination of places 
 where swift and dangerous tidal currents exist; and the deter- 
 mination of the time of occurrence of slack waters when such 
 places may be passed through safely. 
 
 Tide and current surveys have been made in a number of 
 important harbors and waterways in the United States. The 
 data derived from these surveys are ma'de available, through 
 a series of special publications which give in considerable 
 detail the results of the observational data, as follows: 
 
 Special Pub. 111. Tides and Currents in New York 
 
 Harbor (1935) 
 Special Pub. 127. Tides and Currents in Southeast 
 
 Alaska (1927) 
 Special Pub. 142. Tides and Currents in Boston 
 
 Harbor (1928) 
 Special Pub. 150. Tides and Currents in Portsmouth 
 
 Harbor (1929) 
 Special Pub. 162. Tides and Currents in Chesapeake 
 
 Bay (1930) 
 Special Pub. 174. Tides and Currents in Long Island 
 
 and Block Island Sounds (1932) 
 Special Pub. 180 . Tides and Currents in Hudson 
 
 River (1934) 
 
Special Pub. 208. Currents In Narragansett Bay, 
 Buzzards Bay, Nantucket and 
 Vineyard Sounds (1938) 
 
 Special Pub. 211. Currents In St. Johns River , 
 
 Savannah River, and Intervening 
 Waterways (1938) 
 
 TIDE AND CURRENT TABLES 
 
 Tide Tables . -- Advance information relative to the rise 
 and fall of the tide is given in annual tide tables. These 
 tables include the predicted times and heights of high and 
 low waters for each day in the year for a number of reference 
 stations and differences for obtaining similar predictions for 
 numerous other places. 
 
 Current Tables. -- Accompanying the rise and fall of the 
 tide is a periodic horizontal flow of the water known as the 
 current. Advance information relative to these currents is 
 made available in annual current tables which include daily 
 predictions of the times of slack water and the times and 
 velocities of strength of flood and ebb currents for a number 
 of waterways, together with differences for obtaining predic- 
 tions for numerous other places. 
 
 Publications issued annually are: 
 
 Tide Tables, Europe and West Coast of Africa (in- 
 cluding Mediterranean Sea) 
 
 Tide Tables, East Coast, North and South America 
 (including Greenland) 
 
 Tide Tables, West Coast, North and South America 
 (including Hawaiian Islands) 
 
 Tide Tables, Central and West Pacific Ocean and 
 Indian Ocean 
 
 Current Tables, Atlantic Coast, North America 
 
 Current Tables, Pacific Coast, North America, and Asia 
 
 TIDAL CURRENT CHARTS 
 
 Each of these publications consists of a set of 12 charts 
 which depict, by means of arrows and figures, the direction and 
 velocity of the tidal current for each hour of the tidal cycle. 
 The charts, which may be used for any year, present a compre- 
 hensive view of the tidal current movement in the respective 
 waterways as a whole and also supply a means of readily deter- 
 mining for any time the direction and velocity of the current 
 at various localities throughout the water areas covered. 
 
The New York Harbor tidal current charts are to be used 
 with the annual tide tables. The other charts require the 
 annual current tables. 
 
 Tidal Current Charts, Boston Harbor 
 
 Tidal Current Charts, Narragansett Bay to Nantucket 
 
 Sound 
 Tidal Current Charts, Long Island Sound and Block 
 
 Island Sound 
 Tidal Current Charts, New York Harbor 
 Tidal Current Charts, Delaware Bay and River 
 Tidal Current Charts, Tampa Bay 
 Tidal Current Charts, San Francisco Bay 
 Tidal Current Charts, Puget Sound, Northern Part 
 Tidal Current Charts, Puget Sound, Southern Part 
 
 TIDAL BENCH MARKS 
 
 To provide permanent reference points for the observed 
 heights of the tide and the tidal datum planes determined 
 therefrom, a system of bench marks is established at each 
 tide station. The descriptions and elevations of these bench 
 marks along our coasts are compiled by states and localities, 
 and published for free distribution. Requests for such bench 
 mark data should specify the coastal locality for which the 
 information is desired. 
 
 TEMPERATURE AND DENSITY OF SEA WATER 
 
 Daily observations of the temperature and density of sea 
 water are obtained by the Coast and Geodetic Survey, usually 
 at its tide stations, and the monthly and yearly mean and 
 extreme values are given In the following publications, which 
 are available without charge 
 
 SURFACE WATER TEMPERATURES, ATLANTIC AND GULF COASTS 
 Publication No. TW-1 
 
 SURFACE WATER TEMPERATURES, PACIFIC OCEAN, Publication 
 No. TW-2 
 
 DENSITY OF SEA WATER, ATLANTIC AND GULF COASTS, Pub- 
 lication No. DW-1 
 
 DENSITY OF SEA WATER, PACIFIC OCEAN, Publication No. DW-2 
 PUBLICATIONS OF GENERAL INTEREST 
 
 Other publications of a more general nature which are 
 related to the subjects of tides and currents are as follows: 
 
MANUAL OF HARMONIC ANALYSIS AND PREDICTION OF TIDES. 
 Paul Schureman. Special Pub. 98. Revised 1940. 321 p. 
 34 lllus. 
 
 MANUAL OF TIDE OBSERVATIONS. Special Pub. 196. 
 Revised edition (l94l). 96 p. 30 lllus. 
 
 MANUAL OF CURRENT OBSERVATIONS. Special Pub. 215. 
 Revised 1950. 93 p. 36 illus. 
 
 TIDE AND CURRENT GLOSSARY. Paul Schureman. Special 
 Pub. 228. Revised 1949. 43 p. 
 
 COASTAL CURRENTS ALONG THE ATLANTIC COAST OF THE 
 UNITED STATES. F. J. Haight . 1942. 77 p. 35 illus. 
 15 tables. 
 
 TIDAL HARMONIC CONSTANTS, ATLANTIC OCEAN, INCLUDING 
 ARCTIC AND ANTARCTIC REGIONS. Pub. TH-1. 1942. 
 141 p. 
 
 TIDAL HARMONIC CONSTANTS, PACIFIC AND INDIAN OCEANS. 
 Pub. TH-2. 1942. 133 p. 
 
 CHART. - SEISMIC SEA WAVE TRAVEL TIMES TO HONOLULU. 
 
 The chart shows by a series of concentric circular lines 
 overprinted in red the time required for a seismic sea wave 
 to travel from an epicenter anywhere in the Pacific Ocean to 
 Honolulu. 
 
MAGNETIC DATA 
 
 The magnetic work of the U.S. Coast and Geodetic Survey, 
 begun as one of the essential operations in the preparation 
 of nautical charts of coastal waters, has been extended to 
 cover the interior of the United States, thus answering the 
 needs of the land surveyor, the airman, the geophysical pros- 
 pector using magnetic methods, and the scientist ■ working on 
 problems associated with terrestrial magnetism. 
 
 Surveying by compass, though not to be compared with 
 more accurate methods, does have advantages of speed and sim- 
 plicity, and is sometimes the best means of retracing old lines. 
 Many of the early surveys were run with the compass. 
 
 The compass does not, in general, point to true (geo- 
 graphic) north, nor is its direction at any one place constant. 
 Hence, a knowledge of the magnetic declination (compass varia- 
 tion) and its changes is required by those who use the compass. 
 
 The Coast and Geodetic Survey has made a magnetic survey 
 of the United States, in which observations have been made at 
 nearly every county seat and at many other places. In addition, 
 the changes of the earth's magnetism have been determined from 
 the repeat observations made at about 150 selected stations dis- 
 tributed over the country, and from the continuous photographic 
 records of magnetic declination and intensity made at magnetic 
 observatories maintained by the United States and adjoining 
 countries. The observatories operated at the present time by 
 the Coast and Geodetic Survey are at Cheltenham, Md.; Honolulu, 
 T.H. ; San Juan, P.R. ; Sitka, Fairbanks, and Barrow, Alaska; 
 and Tucson, Ariz. (See Plate I.) 
 
 The magnetic survey of the United States dates back over 
 a century. The observations were at first confined to the 
 coastal regions, as they were intended to provide magnetic 
 data for nautical charts. The work was later extended to the 
 interior of the country, and was greatly expanded and intensi- 
 fied at about the turn of the century. There are now more 
 than 8500 stations at which observations of one or more magnetic 
 elements have been taken. In many regions they bring out 
 clearly the widespread irregularities that effect the magnetic 
 lines . 
 
 Information on the gradual change in direction of the 
 compass needle, essential in working with old surveys, has been 
 derived from many sources, including the reports of observations 
 made in very early times in various regions. Tables of this 
 secular change are available, together with explanations of 
 their use. This change cannot be predicted, nor can it be 
 reduced to any simple mathematical law or formula. 
 
Due to the local irregularities already mentioned, it 
 is not possible to give an accurate value of the declination 
 at a specific point unless it has been actually measured at 
 that point. Lacking actual observations, the best estimate 
 may be obtained from the latest isogonic chart of the United 
 States. A value so obtained may be regarded as a kind of 
 normal or mean value for a fair-sized region around the point 
 in question. There is perhaps an even chance that the chart 
 value will be within one-half degree of the actual value. The 
 value is intended as a mean for several days, eliminating 
 diurnal and irregular fluctuations. 
 
 The daily variation of declination in the United States 
 is characterized by an easterly motion of the north end of 
 the needle in the morning, with an easterly extreme about 8 
 or 9 a.m., local time; then a westerly motion, with a westerly 
 extreme about 1 or 2 p.m.; then an easterly motion for 4 or 5 
 hours. Prom dusk to the early morning there is little change. 
 The average amplitude of the swing from morning to afternoon 
 is usually between 5" and 10" of arc, being greater in summer 
 than in winter, and greater at the 11-year peak of sunspot 
 activity than at its trough. Both the amplitude and the times 
 of the extremes are also subject to some fluctuation from day 
 to day. Similar but opposite changes are found at corres- 
 ponding latitudes in the Southern Hemisphere. 
 
 Aside from this systematic daily variation, the direction 
 of the needle occasionally undergoes erratic fluctuations which, 
 if sufficiently severe, constitute a magnetic storm. The 
 surveyor should be on the lookout for such an occurrence. 
 Any unusual activity of the compass needle may have this ex- 
 planation. Surveys made during the progress of a magnetic 
 storm could be seriously in error, as the declination is then 
 usually changing rapidly, and departures from normal of as 
 much as half a degree may easily occur in the middle latitudes. 
 During the great magnetic storm of September 18 and 19, 194l s 
 the maximum range of the fluctuations amounted in this region 
 to more than 4° of arc. A magnetic storm may last many hours 
 (sometimes several days) and the more severe ones are known 
 to extend from pole to pole over the entire globe. They are 
 usually associated with the appearance of aurora and with other 
 phenomena of the ionosphere. They have no apparent relation 
 to the weather. 
 
 The following publications are illustrative of the material 
 that is provided in this field: 
 
 MAGNETIC DECLINATION IN THE UNITED STATES, 1945. 
 Samuel A. Deel. Serial 664. 67 p. 4 Illus* 
 Includes tables of secular change and directions 
 for finding the true meridian, also a copy of 
 Chart 3077 for 1945- 
 
UNITED STATES MAGNETIC TABLES AND MAGNETIC CHARTS 
 FOR 1945. Samuel A. Deel and H. Herbert Howe. 
 Serial 667. 137 p. 5 illus. Includes observed 
 values and positions of the stations. 
 
 MAGNETISM OP THE EARTH. Albert K. Ludy and H. 
 Herbert Howe. Serial 663. 83 p. 39 illus. (19^5) 
 A general review of the whole field. 
 
 ISOGONIC CHART FOR 1950, UNITED STATES. (Chart 
 3077) Scale 1:5,000,-000. 
 
DEPARTMENT OF COMMERCE 
 COAST AND GEODETIC SURVEY 
 
 SEISMOLOGICAL SERVICE 
 
 EARTHQUAKE HISTORY, seismograph operation and earthquake 
 location, mapping of earthquake areas, recording and analyzing de- 
 structive earthquake motions for use in design of earthquake-resistant 
 structures. Special studies of general vibrations affecting foundations 
 and structures. 
 
 FIELD WORK 
 
 General Earthquake Studies 
 21 Seismological stations of Bureau 
 
 Surveys of earthquake areas 
 Returns from questionnaire program 
 
 Engineering Seismology 
 
 Strong- motion recording stations 
 
 Special Vibration Work 
 
 -SOURCES OF DATA- 
 
 OTHER INFORMATION 
 
 Data from cooperating stations 
 
 Reports from State Collaborators, 
 
 cooperating employees of Government, 
 
 and industrial organizations and private 
 
 individuals 
 
 Reports from Associations of 
 
 Architects and Structural Engineers 
 
 WASHINGTON OFFICE WORK 
 
 Compilation of earthquake data 
 
 Compilation and analysis of seismograms 
 
 Compilation and analysis of strong- motion data 
 
 Analysis of ground and building vibration records 
 
 Publication of results 
 
 PRINCIPAL USERS 
 
 Designing engineers for Earthquake-Resistive construction 
 
 Governmental Agencies for special foundation problems 
 
 Industrial and Engineering organizations for special vibration problems 
 
 Insurance companies in setting insurance rates 
 
 Local governments in drafting building codes 
 
 Meteorologists for research on storm paths as related to ground vibrations 
 
 Geologists for location of active faults in earth's crust 
 
 Geophysicists for research on subcrustal structures 
 
 Oceanographers in study of seismic sea waves 
 
 Seismologists in fundamental research 
 
 General public for miscellaneous purposes 
 
SEISMOLOGICAL DATA 
 
 In 1925 the Coast and Geodetic Survey was designated by 
 law to make reports and investigations in seismology. The 
 purpose of this work is to map earthquake areas and evaluate 
 earthquake risk through the operation of seismographs and the 
 systematic collection of earthquake information; to furnish 
 authentic earthquake information to the public; to furnish 
 important data to geophysicists working on research problems; 
 to furnish the basic ground-motion data on destructive earth- 
 quakes for the use of the structural engineer in designing 
 structures in earthquake areas; and to investigate the scien- 
 tific aspects of earthquakes for a better understanding of the 
 principles underlying their cause, frequency, and distribution. 
 
 In order to map earthquakes the Survey supervises the 
 operation of 28 Bureau and cooperating stations and also -uti- 
 lizes data from about 153 other stations. The Survey obtains 
 telegraphic data from seismograph stations all over the world 
 and issues prompt reports on earthquake locations. Scientific 
 study of these data yields information on the true nature of 
 earthquake phenomena, the nature of seismic wave propagation, 
 and the physical structure of the Earth. Seismic waves serve 
 as a kind of X-ray to reveal complexities in the Earth's struc- 
 ture which would otherwise never be known. When strong earth- 
 quakes occur the shaken areas are canvassed for information on 
 damage and other effects. The results of all of these opera- 
 tions are published in periodic reports. 
 
 Fifty-two seismographs of special design are operated 
 in earthquake areas to obtain information on destructive ground 
 motions needed by the engineer to construct safe buildings, 
 bridges, dams, et cetera. Because of the technical diffi- 
 culties involved in applying this information to building de- 
 sign, the project must be considered still in the research 
 stage. 
 
PENN STATE UNIVERSITY LIBRARIES 
 
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