U.S. Geological Survey Manual
OPR: National Mapping Division
1. Purpose. This chapter defines the products of the National Mapping Program and states the basic standards to be followed in their preparation. Detailed technical specifications relating to each map series, and to the production of digital cartographic data, are contained in the Technical Instructions of the National Mapping Division.
2. Products. The National Mapping Program includes the individual map series and digital map data listed below, which are produced and distributed by the Geological Survey.
A. Maps. Selected maps in some series may be produced at additional scales.
7.5-minute series (at 1:24,000 or 1:25,000 scale in the 50 States, 1:20,000 scale in Puerto Rico)
15-minute series (1:63,360 scale - Alaska)
30-by 60-minute series (1:100,000 scale)
1$ by 2$ series (1:250,000 scale)
Land Use and Land Cover Maps (1:100,000 or 1:250,000 scale)
Orthophotomaps (1:24,000 or 1:25,000 scale)
Orthophotoquads (1:24,000 or 1:25,000 scale; 1:63,360 scale in Alaska)
County Maps (1:50,000 or 1:100,000 scale)
State Base Maps (1:500,000 scale)
National Atlas General Reference Maps (1:2,000,000 scale)
U.S. Base Maps (1:2,500,000 through 1:16,500,000 scale)
National Park Maps (various scales)
Antarctic Maps (1:50,000 through 1:1,000,000 scale)
Miscellaneous Maps (special areas at various scales)
Maps in the following series are generally not revised or reprinted:
15-minute series (1:62,500 scale)
30-minute series (1:125,000 scale)
1$ by 1$ series (1:250,000 scale)
Alaska Reconnaissance Maps (interim 1:250,000 scale)
Metropolitan Area Maps (1:24,000 scale)
International Map of the World (1:1,000,000 scale)
U.S. Map Series (1:1,000,000 scale)
Copies of these maps, and maps replaced by revision, are held in the National Mapping Division's historical file. Monochrome copies are supplied to the public on request at the cost of reproduction. Additional graphic and digital map products may be established as needed.
B. Digital Data.
7.5-minute Digital Elevation Models (DEMs)
15-minute DEMs (Alaska)
30-minute DEMs (48 States and Hawaii)
1$ Digital Terrain Elevation Data (DTED) (Defense Mapping Agency product, produced and distributed by the Geological Survey)
1:24,000-scale Digital Line Graphs (DLGs)
Land Use and Land Cover digital data (1:100,000 or 1:250,000 scale)
Geographic Names Information System data bases.
3. Graphic Products.
A. Coverage. Complete coverage of the United States exists or is planned for the 1:250,000-scale, State base map, and 1:2,000,000-scale series. Complete coverage at 1:24,000 or 1:25,000 and 1:100,000 scale is planned for the conterminous United States and Hawaii. Complete 1:63,360-scale coverage is planned for Alaska; 1:24,000- and 1:25,000-scale coverage in Alaska produced in areas of special need.
B. Editions. Maps in the following editions are prepared and printed for distribution:
(1) Topographic. This edition contains all base map category planimetric and hypsographic information.
(2) Topographic-bathymetric. This edition is the topographic edition with bathymetric contours included in coastal areas where available.
(3) Topographic-provisional. This edition contains essentially the same level of information as the standard topographic edition, but differs somewhat in symbolization and appearance. Prepared by modified procedures in which map-finishing operations are significantly reduced, this edition is produced to expedite completion of map coverage of areas in the continental United States not yet covered by standard edition 1:24,000- or 1:25,000-scale topographic maps.
(4) Orthophotomap. This edition includes an aerial photographic image, scale-corrected and printed in true ground position. The image base is printed in different colors according to feature and is overprinted with contours and other standard map symbols.
(5) Shaded Relief. This edition includes a shaded overprint that provides a three-dimensional impression of the terrain. Shaded relief treatment is applied only to selected maps.
(6) National Atlas of the United States. The National Atlas is a comprehensive collection of maps portraying geographic patterns of significant physical, economic, sociocultural, administrative, and historical characteristics of the Nation. The thematic or special subject maps, presented on a common projection and at the basic scales of 1:7,500,000, 1:17,000,000, and 1:34,000,000, convey concepts of man-environment relationships and provide bases for reference and research use. A set of 1:2,000,000-scale sectional reference maps is also included.
(7) Other Editions. Maps in some series are published in editions that vary from those described above. Examples are the United States, State base, and national park maps. Selected topographic edition maps are printed back-to-back with satellite image maps of the same area. Sometimes, custom maps are designed and compiled to meet the needs of a special project or program of another Federal agency or State cooperator.
C. Other Graphic Products. The following map products generally are not printed, but are prepared and made available through other forms of publication:
(1) Orthophotoquad. This edition portrays planimetric data by a photoimage in true ground position, but contains no symbolized features, including contours. A minimal number of names are shown within the mapped area. Orthophotoquads are prepared in monochrome and are made available in the form of diazo or photographic prints.
(2) Land Use and Land Cover Maps and Associated Maps. These maps portray land use and land cover data in polygon format at 1:250,000 scale and in selected areas at 1:100,000 scale that were derived from aerial photographs in accordance with specifications contained in Geological Survey Professional Paper 964 and Open-File Report 77-555. Also produced are associated maps delineating political units, hydrologic units, Census county subdivisions, and in some cases Federal and State land ownership. Land use and land cover maps and associated maps are made available as Geological Survey Open-File Reports (L series).
D. Quadrangle Formats. The standard quadrangle formats are 7.5 by 7.5 minutes, 7.5 by 15 minutes, 15 by 15 minutes, 30 minutes by 1$ , and 1$ by 2$ in latitude and longitude, respectively, within the conterminous United States. For special areas, usually outside the conterminous States or along coastlines, quadrangle formats are adjusted to account for such conditions as convergence of meridians in polar regions, the size and location of islands, and irregular coastlines or boundaries.
E. Datums. Geological Survey maps generally conform to the datums established in the area covered.
(1) Horizontal Datums. The horizontal datum defines the size and shape of the Earth and the latitude and longitude coordinate system. Thus the horizontal datum controls the position of mapped features with reference to the parallels and meridians, and grid ticks or lines shown on topographic maps. Examples of horizontal datums used on Geological Survey maps of the United States include:
North American Datum of 1927 (NAD 27)
Old Hawaiian Datum (OHD)
Puerto Rico Datum (PRD)
North American Datum of 1983 (replaces NAD 27, OHD, and PRD)
To extend the useful life of a map whose horizontal datum has been superseded, ticks are added to indicate the location of the graticule on the new datum and an explanatory footnote is added that provides corrections required to place the map on the new datum. When a map is produced on a new datum, ticks are added to indicate the location of the graticule on the superseded datum and an explanatory footnote is added that provides corrections required to place the map on the superseded datum.
(2) Vertical Datums. The vertical datum provides a surface of reference for determining point elevations and for compiling contours. The mean sea level surface, measured by tide gauges, is generally the zero point for vertical datums. Vertical datums used on Geological Survey maps of the United States include:
Mean Sea Level
Mean Sea Level of 1929
National Geodetic Vertical Datum of 1929
An explanatory footnote that provides a correction to a new datum is added to maps whose vertical datum has been superseded.
F. Grid Reference Systems. Grid Reference Systems that have been established by other Federal agencies, such as the National Geodetic Survey and the Defense Mapping Agency, are generally indicated on Geological Survey maps by ticks along the neatlines or by lines extending across the map. The purpose of these grids is to make the map more usable by providing a Cartesian positioning system as an alternative to geodetic latitude and longitude. The State Plane Coordinate System is indicated on all maps of 1:250,000 scale and larger of areas within the 50 States and U.S. territories. In addition, a full, fineline Universal Transverse Mercator grid is shown on new maps at scales of 1:1,000,000 and larger. Older maps and maps of foreign areas generally do not show either coordinate system.
G. Contour Intervals. Contours, lines connecting points of equal elevation above a vertical datum, portray terrain relief. Because of the wide variation of relief, it is impractical to specify a single contour interval for a given map series. Therefore, contour intervals are established as follows:
(1) Basic. The basic contour interval is selected for each map to most clearly portray the predominant terrain of the area. Basic intervals for the 7.5-minute and 15-minute series are 5, 10, 20, 40, and 80 ft; for the 1:250,000 and Alaska 1:63,360 series, 25, 50, 100, and 200 ft; for maps with metric intervals, 1, 1.5, 2, 3, 4, 5, 6, 10, and 12 m. For map scales smaller than 1:250,000, larger contour intervals are used. More than one basic interval may be used on maps of areas containing abrupt contrasts in relief, provided that an adequate explanation is given in the legend.
(2) Supplementary. Contours that subdivide the basic interval are used where needed for adequate portrayal of the terrain. In the portions of maps where supplementary contours are used, both the basic and supplementary contours must meet the accuracy standards for the smallest interval.
(3) Underwater. Contours compiled before areas are inundated by the construction of dams are retained as useful hypsographic information. These areas are overprinted with the standard water tint.
(4) Bathymetric Contours. A bathymetric contour is a line connecting points of equal water depth. Bathymetric contours in meters are shown at varying intervals on standard topographic maps of coastal areas whenever adequate data can be obtained from hydrographic surveys of the National Ocean Service. The datum for bathymetric contours in tidal waters of the Atlantic Coast, Gulf of Mexico, and Pacific Coast, including Alaska and Hawaii, is mean lower low water. The datum for inland water bodies varies and is noted on the map. On navigable rivers above tidal reaches, the datum conforms to the stream gradient.
H. Accuracy. Geological Survey maps at scales of 1:250,000 or larger are prepared by methods designed to meet the National Map Accuracy Standards, Appendix A. These standards were issued by the former Bureau of the Budget and are quoted in full in the appendix. In certain obstructed or inaccessible areas, such as densely wooded terrain, full compliance with the standards may not be feasible.
(1) Accuracy Testing and Checking. Maps are checked for compliance with horizontal and vertical accuracy standards by methods and procedures specified in the Technical Instructions of the National Mapping Division. In evaluating map accuracy in statistical terms, an appropriate value of allowable standard error (root-mean square) may be used.
(2) Certification. A series of checks, tests, and a knowledge of the compilation history of the map determines whether or not a map will be certified as meeting accuracy standards. If a map does not meet standards, remedial action is taken, if feasible, or a recommendation is made to omit the accuracy statement in the map legend. The decision regarding the omission of the accuracy statement is the responsibility of the Chief of the Mapping Center, who promptly advises the Chief, National Mapping Division, in writing, of the reasons for his decision. Maps certified as meeting the standards carry the marginal note "THIS MAP COMPLIES WITH NATIONAL MAP ACCURACY STANDARDS."
I. Revision. Published maps must be revised periodically to preserve their usefulness. Three types of revision are used. The choice depends on user requirements for individual quadrangles or projects.
(1) Complete Revision. The correction of all deficiencies in planimetry and relief, including updating map content and improving, if necessary, horizontal and vertical accuracy to produce a map meeting current specifications. A field check is required.
(2) Limited Revision. The correction of specified map deficiencies and the updating of selected map content. The revised data appear on the published map in conventional colors. A field check may be required.
(3) Photorevision. The updating of a map, from aerial photographs and other available sources, to reflect planimetric changes that have occurred since the date of the latest published map. The revised data are not field checked and are printed in purple on the new map.
4. Digital Products.
A. Digital Data Types. Digital map data are produced as: (1) Digital Line Graphs (DLGs) containing selected base category and other data digitized as points, lines, and areas and organized in files (public land survey system, boundaries, hydrography, transportation, other significant man made structures, hypsography, surface cover, non vegetative surface features, and survey control and markers); and (2) Digital Elevation Models (DEMs) consisting of an array of elevations for ground positions spaced at regular intervals. Also produced in digital form are data on published land use and land cover and associated maps, and on geographic names from the Geographic Names In formation System.
B. Coverage. Complete coverage of the continental United States, Hawaii, and Puerto Rico is planned for the 1:24,000- and 1:100,000-scale DLGs. Partial coverage for Alaska in the form of 1:63,360-scale DLGs and 15-minute DEMs is available and will be extended as required. Coverage in the 1-degree DEM format is complete for the entire United States. A 30-minute DEM series also is being produced.
C. Data Content and Format.
(1) Digital Line Graphs (DLGs). Geological Survey map products are used as a source for DLG data at scales ranging from 1:20,000 in Puerto Rico to the 1:2,000,000-scale sectional maps from the National Atlas of the United States of America. See paragraph 800.2.2 for specific scales and products.
(2) Digital Elevation Models (DEMs). Four DEM data products are prepared:
(a) 7.5-minute DEMs with 30-meter grid spacing are derived from automatic photogrammetric correlation of stereo aerial photography, from manual profiling of stereo aerial photographic models or from interpolation of DLG contours digitized from 1:24,000- or 1:25,000-scale map materials. Each product provides the same coverage as a standard Geological Survey 7.5-minute series quadrangle. This product also includes the Alaska series 7.5-minute DEMs obtained from digitized contours and drainage information on 1:24,000- or 1:25,000-scale maps. The data spacing is 1 arc-second of latitude by 2 arc-seconds of longitude. The latitudinal extent of each DEM is 7.5 minutes; however, the longitudinal extent varies from 10 minutes at the southern most latitude of Alaska to 18 minutes at the northernmost latitude.
(b) 15-minute DEMs in Alaska are derived primarily from DLG contours digitized from 1:63,360-scale map materials. The data spacing is fixed at 2 arc-seconds of latitude by 3 arc-seconds of longitude. The latitudinal extent of each DEM is 15 minutes and the longitude extent varies from 20 minutes at the southernmost latitude of Alaska to 36 minutes at the northernmost latitude of Alaska.
(c) 30-minute DEMs are 2- by 2- arc-second grid arrays providing the same coverage as one-half the area of a Geological Survey 30- by 60-minute quadrangle. Interim 30-minute DEMS are created for selected areas from available 7.5 minute DEMs. The interim products will be replaced by 30-minute DEMs derived from DLG contours digitized from 1:100,000-scale map materials. The saleable unit is a 30-minute block consisting of four 15- by 15-minute DEM files. This product is intended as a companion product to the 1:100,000-scale DLG.
(d) 1-degree DEMs and Defense Mapping Agency DTED are 3- by 3-arc- second grid arrays providing the same coverage as one-half (1$ by 1$) of a standard Geological Survey 1$ by 2$ quadrangle. They are derived from contours digitized from these map materials.
The Defense Mapping Agency DTED (1$ DEMs) covering the conterminous United States are being replaced. The Geological Survey, through a cooperative agreement with the Defense Mapping Agency, prepares the new DTED for selected areas from 7.5 and 30-minute Geological Survey DEMs.
(3) Land Use and Land Cover and Associated Maps. These maps consist of land use and land cover and associated political unit, hydrologic unit, census county subdivision, Federal land ownership, and State land ownership information.
(a) Land Use and Land Cover Maps provide data useful either alone or in combination with the associated data sets or other base category data. The basic sources of land use compilation data are high-altitude aerial photographs, usually at scales smaller than 1:60,000. The 1:250,000-scale topographic map series is generally used as the base map for compilation. Land Use and Land Cover features are delineated by curved or straight lines that depict the actual boundaries of the areas (polygons) being described. Minimum 4-hectare (ha) polygons show such classes as urban or built-up land, water, confined feeding operations, other agricultural land, strip mines, quarries, gravel pits, and urban transitional areas. All other classes have a minimum polygon size of 16 ha.
(b) Political unit maps portray county, independent city, and State boundaries and their numerical codes.
(c) Census county subdivision maps depict boundaries and numerical codes for either census tracts in Standard Metropolitan Statistical Area (SMSA) counties before June 1983, or minor civil divisions (or equivalent divisions) in non-SMSA/Metropolitan Statistical Area/Primary Metropolitan Statistical Area counties.
(d) Hydrologic unit maps are based on area delineations published by the Geological Survey Office of Water Data Coordination. The hydrologic units include an eight-digit number that indicates the hydrologic region, subregion, accounting unit, and cataloging unit.
(e) Federal land ownership maps include minimum 16-ha polygons obtained by the Geological Survey from plats and other descriptive data related to Federal land ownership provided by other Federal agencies.
(f) State land ownership maps are included in some instances where a cost-sharing cooperative agreement was reached with a State to publish polygons encoded according to a reference system used by the State.
(4) Geographic Names Information System. This system is currently composed of four data bases:
(a) National Geographic Names Data Base.
(b) Geological Survey Topographic Map Names Data Base.
(c) Reference Data Base.
(d) Board on Geographic Names Data Base.
The initial compilation of geographic names, or phase I, is complete and includes records for most named features on all maps in the Geological Survey topographic map series except for roads and highways. Maps of the largest scale available were used during the initial compilation. The majority of the names were compiled from 1:24,000 scale, 7.5-minute topographic maps. A report listing each name is available in the form of bound listings, microfiche, or magnetic tape. Specialized reports tailored to individual user needs also are available. The geographic names in each State and territory are published as separate volumes in the National Gazetteer of the United States after phase II, the systematic collection of names from additional sources, including maps, charts, and texts, as well as historical sources, is completed.