Common Terms


A common USGS Scale. Also known as 1:100,000 or 1 inch on the map equals 100,000 inches on the earth. (1 inch = 8333.33 feet = 1.57828 miles).


A common USGS Scale. Also known as 1:24,000 or 1 inch on the map equals 24,000 inches or 2,000 feet on the earth. This is usually considered a large scale (1/24,000). 1 inch = 2000 feet = 0.37878 miles).


A common USGS Scale. Also known as 1:250,000 or 1 inch on the map equals 250,000 inches on the earth. This is usually considered a small scale (1/250,000). 1 inch = 3.945707 miles).

3 Arc Second

Three seconds of latitude or longitude. Approximately 90 meter resolution in North America (~60-meters in Alaska) and varies based on latitude.

7.5 Minute (7.5′)

A common USGS area of extent used with 1:24,000 topographic maps (or quads). Implies 7.5 minutes of latitude by 7.5 minutes of longitude. Approximately 7 x 9 miles.


The degree in which a measured value is correct.

Aerial Photography

A photograph of the Earth’s surface taken with a camera that is mounted on the airplane.


Attributes describe map information represented by a point, line, or area. For example, an attribute for an area might identify it to be a lake or county; an attribute for a line might identify it as a road, railroad, stream, or shoreline.


Information found on the border or around the edges of a topographic map outside of the map content itself. This information includes: Quadrangle Name, Year of Publication, Corner Coordinates, Projection, etc.


Refers to rasters that have no edge or border information. Collarless rasters are needed for mosaicking multiple rasters together, thus allowing one to create a seamless digital map of a very large area.

Color Infrared Photo (CIR)

CIR film is manufactured in a way that makes it more sensitive to the near-infrared portion of the spectrum. On a CIR photo, infrared energy is represented by tones of red. It is most commonly used for vegetation studies.

Contact Print

Describes a photograph produced directly from a negative of the same size.

Control Point

Features of known ground location that can be accurately located on imagery.


Line of equal elevation.


Digital Elevation Model. A digital file containing equally spaced elevation points represented with an X (east-west value), a Y (north-south value) and a Z (elevation value).


Digital Line Graph. A vector format used widely by the USGS in the 1980s and 1990s. Since replaced by SDTS.


Digital Orthophoto Quad. A USGS Aerial Photo product of One-Meter resolution. 7.5’ Area, Created from NAPP Photography.


Digital Orthophoto Quarter Quad. A USGS Aerial Photo product of One-Meter resolution. 3.75’ Area, Created from NAPP Photography.


Digital Raster Graphic. A USGS product. A scanned USGS topographic map.


Defines the size and shape of the earth. NAD 27, 83 and WGS 84 are the most common.

Decimal Degrees

Latitude/Longitude or Geographic coordinates. The degree fraction is shown as a decimal instead of minutes and seconds (eg., 39.125,-104.375)

Degrees Minutes Seconds

Latitude/Longitude or Geographic Coordinates. The earth is divided into 360 degrees(°), where a degree equals 60 minutes(‘) and 60 seconds(“) equals a minute (eg., 39° 7′ 30″, -104 22’ 30”)


A transparent positive on plastic-based or glass-based film used for creating topographic maps.

Digital Print

A computer scan of a contact print or negative. The scale can be changed to meet most needs.


Earth Resources Observation Systems Data Center. EDC is a national archive, production, distribution, and research facility for remotely sensed data and other geographic information. Located in Sioux Falls, SD.


A World DEM dataset with a resolution of 2 minutes. Includes Ocean Depths, released in 2001 by NOAA.


A World DEM dataset with a resolution of 5 minutes. Includes Ocean Depths, released in 1988 by NOAA.


Federal Information Processing Standard. This is a standardized code used by the USGS and the Federal Government.


Data Format – A file type that can be read by a particular software program. Eg., ArcView Software reads .shp or Shape file format.


One meter Aerial Photography of the United States. Created from DOQQs. 1990 – 2000


Geographic Information System. Software program used to analyize spatial data in a variety of ways.


A World DEM dataset with a resolution of 30 Seconds or approximately 900 meters. Does not include Ocean Depths, completed in late 1996. Developed over a three year period through a collaborative effort led by the U.S. Geological Survey.


The scientific study and mapping of the earth’s topography. Sometimes refers to the contour vector layer.

LandSat 5

Satellite launched in March, 1984 as a NASA/USGS initiative. Carries the 30-Meter Thematic Mapper (TM) sensor. Remains in operation today.

LandSat 7

Satellite launched in April, 1999 as a NASA/NOAA/USGS initiative. Carries a new sensor called the Enhanced Thematic Mapper Plus (ETM+). Contains a 15-Meter Panchromatic Band. Remains in limited operation today.

Large Scale

The word ‘Large’ refers to the fraction ‘Units on map / Units on earth’ (eg., 1/24,000). Implies a map or photo showing a high amount of detail but a small area.


Angular distance, in degrees of a point north or south of the Equator. Also thought of as an E-W line parallel to the equater denoting a North or South position.


Angular distance, in degrees of a point east or west of Greenwich, England. Also thought of as a N-S line or meridian denoting an East or West position.


Merging two or more spatial data files into one seamless file.


North American Datum of 1927. NAD27 is defined with an initial point at Meads Ranch, Kansas, and by the parameters of the Clarke 1866 ellipsoid. The location of features on most USGS topographic maps, including the definition of 7.5-minute quadrangle corners, are referenced to the NAD27.


North American Datum of 1983. NAD83 is an Earth-centered datum and uses the Geodetic Reference System 1980 (GRS 80) ellipsoid, unlike NAD27, which is based on an initial point (Meades Ranch, Kansas). Using recent measurements with modern geodetic, gravimetric, astrodynamic, and astronomic instruments, the GRS 80 ellipsoid has been defined as a best fit to the worldwide geoid. Because the NAD83 surface deviates from the NAD27 surface, the position of a point based on the two reference datums will be different.


National Agriculture Imagery Program. Started in 2002 by the USDA. Purpose is to quickly create digital aerial photography at one and two meter resolutions. An emphasis is given to areas containing agricultural land.


National Aerial Photography Program. NAPP was established to coordinate the collection of aerial photography covering the 48 contiguous States and Hawaii every five years. NAPP’s goals are to ensure that photography with uniform scale, quality, and cloud-free coverage be made available to meet the requirements of several Federal and State agencies. The program was initiated in 1980 as the National High Altitude Photography (NHAP) program. In 1987, the program was renamed to NAPP when the flying height for the program changed from 40,000 feet to 20,000 feet. NAPP photography is available in black and white, and in most cases, color-infrared. The program is administered by the U.S. Geological Survey’s National Mapping Division. NAPP imagery is used by the USGS for photo revision and land use land cover characterization work on the standard series maps at 1:24,000; 1:100,000 and 1:250,000 scales.

Natural Color Photos

Aerial photographs produced in natural color are less common and more expensive but can be more useful because the human eye can discriminate between color variations better than shades of gray.


Neatlines separate the body of a map from the map margin. On quadrangle maps, the neatlines are often the latitude and longitude that delimit the quadrangle.

Oblique Photos

These photos are taken with the camera axis at an angle other than 90° to the ground. The image can be a high oblique, which includes a horizon, or a low oblique, which does not.


A reconstructed aerial photo in which all X,Y distortion has been removed.

Orthophoto Mosaic

A mosaic constucted from orthophotos. The image is seamless because the scale variations and distortions have been removed.


Public Land Survey System. The U.S. Public Land Survey System is the most widespread land ownership system in the United States. Land is subdivided by a rectangular system of surveys established and regulated by the Bureau of Land Management. The standard format for subdivision is based on townships measuring 6 miles (480 chains) on a side. Townships are further subdivided into 36 numbered sections of 1 square mile (640 acres) each.

Photo Index

A grid map to reference individual aerial photos.


Four-sided area, bounded by parallels of latitude and meridians of longitude. Usually refers to a topographic map.


A spatial image where the data is expressed as a matrix of cells or pixels, with spatial position implicit in the ordering of the pixels. This data is particularly suitable for certain types of spatial operations (e.g., overlays or area calculations). Unlike vector data, there are no implicit topological relationships.


The process of removing X,Y and Z distortions from a digital aerial photo.


A measure of the amount of detail that can be seen in an image; the earth size of a pixel.


Spatial Data Transfer Standard. The SDTS was approved in July 1992 as Federal Information Processing Standard (FIPS) 173. This Standard is actually a spatial data format used widely by the USGS.


90 Meter global DEM data obtained from the Shuttle Radar Topography Mission. Data obtained in February of 2000.


A spacecraft that orbits another body, such as a planet or the sun.


Relationship existing between a distance on a map and the corresponding distance on the Earth.


Data where the boundaries are defined by the user. Traditionally boundaries have been pre-defined by 7.5′, 30′ x 60′ or 2° x 1° areas of Latitude and Longitude.

Small Scale

The word ‘Small’ refers to the fraction ‘Units on map / Units on earth’ (1/250,000). Implies a map or photo covering a large area but showing a small amount of detail.


Two adjacent, overlapping aerial photos that when viewed together through a stereoscope produce a 3D image.


Thematic Mapper – A Landsat multispectral scanner designed to acquire data to categorize the Earth’s surface. Particular emphasis was placed on agricultural applications and identification of land use. The scanner continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels. Overlaying two or more bands produces a false color image. The ground resolution of the six visible and shortwave bands of the Thematic Mapper is 30 meters, and the resolution of the thermal infrared band is 120 meters. Thematic mappers were flown on Landsat 4 and 5.

Topographic Map

Maps that present the horizontal and vertical positions of the features represented; distinguished from a planimetric map by the addition of relief. the elevation element.


United States Geological Survey. Established in March of 1879, the Geological Survey’s primary responsibilities are: investigating and assessing the Nation’s land, water, energy, and mineral resources; conducting research on global change; investigating natural hazards such as earthquakes, volcanos, landslides, floods, and droughts; and conducting the National Mapping Program. To attain these objectives, the Geological Survey prepares maps and digital and cartographic data; collects and interprets data on energy and mineral resources; conducts nationwide assessments of the quality, quantity, and use of the Nation’s water resource; performs fundamental and applied research in the sciences and techniques involved; and publishes and disseminates the results of its investigations in thousands of new maps and reports each year.


Universal Transverse Mercator projection. This is a very common projection and is used by the USGS. It is based on 6 degree zones of longitude surrounding the earth and the units are in millions of meters.


Vector Map (VMap) Level 0 is an updated and improved version of the National Imagery and Mapping Agency’s (NIMA) Digital Chart of the World (DCW®). The VMap Level 0 database provides worldwide coverage of vector-based geospatial data. The primary source for VMAP0 is the 1:1,000,000 scale Operational Navigation Chart (ONC) series co-produced by the military mapping authorities of Australia, Canada, United Kingdom, and the United States. VMap Level 0 includes major road and rail networks, hydrologic drainage systems, utility networks (cross-country pipelines and communication lines), major airports, elevation contours, coastlines, international boundaries and populated places.


Refers to a format where all spatial data is stored as points, lines, and areas rather than as an image or continuous tone picture (raster). These vector data have location and attribute information associated with them.

Vertical Photos

These are the most common type of aerial photographs. They are produced with the camera axis aimed vertically, perpendicular to the ground.