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.

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.

An American Earth observation satellite launched on February 11, 2013. Originally called the Landsat Data Continuity Mission (LDCM), it is a collaboration between NASA and the United States Geological Survey (USGS).

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.

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.

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.

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

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

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

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.

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.

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

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.

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.

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