Data Collections

Frequently Accessed Data Layers
A collection of commonly used GIS datasets for Tennessee.  Most data are maintained in Tennessee State Plane, NAD83, Units Feet, to enable overlay and integration functions, and are organized by theme.  

Census Data
These data sets are derived from the U.S. Census Bureau's 2000 Redistricting version of the TIGER line files. The population data associated or joined with these files are derived from the Census 2000 Redistricting Data (P.L. 94-171) Summary File. The data includes total and voting age population by racial category at the county, city, and block level geography. Other planimetric layers are also included. 

These data employ the Stateplane coordinate system, NAD 83, Feet.  For more details, please view the following data dictionary.

Digital Orthophoto Quadrangle (DOQQ)
Orthophotos combine the image characteristics of a photograph with the geometric qualities of a map. The primary digital orthophotoquad (DOQ) is a 1-meter ground resolution, quarter-quadrangle (3.75-minutes of latitude by 3.75-minutes of longitude) image cast on the Universal Transverse Mercator Projection (UTM) on the North American Datum of 1983 (NAD83).

DOQ's serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The DOQ is useful as a layer of a geographic information system and as a tool for revision of digital line graphs and topographic maps.

Digital Raster Graphic (DRG)
The Digital Raster Graphic (DRG) is a raster image of a scanned USGS topographic map excluding the collar information. The source maps for DRGs were georeferenced to the UTM grid, but DRG images for Tennessee are available in Tennessee State Plane, NAD83, feet. A DRG is useful as a source or background layer in a GIS, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of DLG data. DRG's can also be merged with other digital data, e.g. DEM's or DOQ's, to produce a hybrid digital file.

Digital Elevation Model (DEM)
Digital elevation model (DEM) data are arrays of regularly spaced elevation values referenced horizontally either to a Universal Transverse Mercator (UTM) projection or to a geographic coordinate system. The grid cells are spaced at regular intervals along south to north profiles that are ordered from west to east. The U.S. Geological Survey (USGS) produces five primary types of elevation data: 7.5-minute DEM, 30-minute DEM, 1-degree DEM, 7.5-minute Alaska DEM, and 15-minute Alaska DEM.