Biological	Features that map the monitoring and the effect of species other than man upon geophysical and environmental features.
Collection	Collection as a theme indicates the file contains multiple features of different themes.
Environmental	Features that map the monitoring and the effect of socio-economic and infrastructure features upon biological and geophysical features.
Geophysical	Features mapping the natural systems of the earth. Climate, soils, geology, and water basins are examples of geophysical features.
Infrastructure	Features that map the structures and edificies built by modern day man for human activities. Roads, buildings, pipelines, and ports are examples of infrastructure features.
Miscellaneous	Any feature not falling within any of the other themes.
Socio-Economic	Features that map elements of human society and the human condition. Demographic features such as tracts and block-groups from TIGER files are examples of such features. Also, governmental divisions such as state and county boundaries are such features. Economic features such as leasing areas are such features.
Reference	Features that aid in locating other features upon the earth. Tiling indices are prime examples of reference features. A feature containing place names is another example.

COT	COntinuous Tone files. This file format is the native file format for a number of applications from Intergraph. Image Analyst and I/RASC from Intergraph use this type of raster file for images. COT files may be compressed using packbits compression. These files may contain image overviews at lower resolution to speed display.
CSV	Comma Separated Values files. This file format is an ASCII file format used by MicroSoft Excel for importing and exporting. In a CSV file, each line represents a row of attributes. Commas separate the attribute values from one another. For example, for the LIDAR point data, each line in a CSV file represents the x, y, and z coordinates of a point. Commas separate the three values.
DBF	Database File format. This file format was made popular by the dBase database management system and is used by ESRI shapefiles for holding attribute data.
DEM	Digital Elevation Models. This file format is a USGS raster file format for delivering elevations data. Many GIS can read and import these files.
DGN	DesiGN Files. This file format is the native file format for the CAD system MicroStation from Bentley Systems. These files are usually vector files. They are used by MicroStation and Intergraph MGE.
DWG	DraWinG Files. This file format is the native file format for the CAD system AutoCAD for AutoDesk. These files are vector files.
DXF	Drawing eXchange File. AutoCAD import/export file. This file is a vector file. It was used by AutoCAD initially to move AutoCAD graphics between different versions of AutoCAD. Other vendors adopted it as a way of moving graphics between different CAD and GIS systems.
E00	Arc/Info export files. These files are vector files. It was used by Arc/Info initially to move Arc/Info coverages between different versions of Arc/Info. Other vendors adopted it as a way of moving GIS data between different GIS systems.
Geomedia	Geomedia Access warehouses. These are MicroSoft Access databases that Geomedia has stored vector graphics.
GeoTIFF	Geographic Tagged Image File Format. These files are TIFF files, which are raster by nature. They differ from ordinary TIF files in that they carry a geographic tag that a number of GIS applications can use to place the image correctly on the earth's surface.
GIF	Graphics interchange format. This compact file format is ideal for graphics that use only a few colors. GIF images are limited to 256 colors. CompuServe developed GIF in 1987, calling it GIF87, and two years later added new features such as interlacing, transparency, and animation to create the format known as GIF89a. People don't usually distinguish between the two GIF versions, so if someone refers to an image as a "GIF89" rather than simply a "GIF," it's probably animated. - paraphased from the About.com glossary resources.
IMG	IMaGine files. This file format is the native file format for ERDAS Imagine. These files are raster files that hold images and raster maps. These files may contain image overviews or pyramids at lower resolution to speed display.
JPG	"Joint Photographic Experts Group file format. Also abbreviated JPEG. This file format for color-rich images was developed by the Joint Photographic Experts Group committee. JPEG compresses graphics of photographic color depth better than competing file formats like GIF, and it retains a high degree of color fidelity. This makes JPEG files smaller and therefore quicker to download. You can choose how much to compress a JPEG file, but since it is a lossy format, the smaller you compress the file, the more color information will be lost." - from the About.com glossary resources.
Mapinfo	Mapinfo vector files. Each layer or feature in MapInfo is represented by four files.
MrSid	MultiResolution Seamless Image Database files. These files are compressed raster files using a compression technology from LizardTech. There is some loss of data with MrSid compression, but, depending on the amount of compression, the loss may not be noticable with the human eye.
Shapefiles	ArcView Shape files. These files are vector files. This file format is the native file format for ArcView version 2 and above. Each layer or feature is represented by at least three files. There is usually a .dbf and a .shp file for each layer.
TIFF	Tagged Image File Format. These are raster files. Many applications including non-mapping systems can read TIF files. The TIF format has become an industry standard for storing images.