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Details About GIS File Formats Available on the Water Resource NSDI Node

Compression and File Formats

.zip is a compressed archive that can be opened using most operating systems. In Windows XP, simply right click on the file in Windows Explorer and select Extract. There are many personel computer software utilities available that work with zipfiles, including WinZip®, PKZIP®, Power Archiver®, WinRAR®, along with open-source zip and unzip commands available on most unix implementations.

.gz are compressed files created using the open-source gzip program available on most computer platforms. The best way to extract them is to use the gunzip program, which normally comes with gzip.

.tar is unix archive (not compression) format.
Tar files can be opened on unix machines using the “tar” utility: tar xvof filename.tar
The Winzip and other utility programs on Windows can open tar files.

.tgz, .tar.gz are extensions that are totally equivalent. These files are tar archives that have been created and then compressed with gzip. They can be extracted using the commands: gunzip –v file.tgz tar xvof file.tar
Alternatively you can do this in one step on a unix system (or a windows system that has tar and gzip installed) gunzip –cv file.tgz | tar xvof –

.e00 are ArcInfo interchange files, also known as “export” files. This is an ascii transfer format that is proprietary to ESRI. The .e00 format can store a variety of GIS data sets, including coverages, tables, symbol sets, and grids. Several systems support the .e00 format, and some GIS systems have reverse-engineered the format so support .e00 format/ ArcGIS: Coverage Tools/Import from Interchange File ArcView 3.x: the IMPORT71.exe utility comes with the software.

.shp, .shx, .dbf are files normally archived together in the tar format, and together make up ESRI’s shapefile format. Most GIS programs can read .shp files, as long as their related ancillary files (.shx, .dbf at the minimum) exist in the same folder as the .shp file. Occasionally non-GIS users open the .dbf files in a spreedsheet application just to view the row-column data.

.bil, .hdr, .blw are binary raw image formats, many GIS systems can read these images assuming the .bil and .hdr files are both in the same folder. The .blw file is used to georeference the image to geographic coordinates (instead of row-column locations).

.tif, .tfw are TIFF image format, supported by many software systems. The tfw file is sometimes used for image georeferencing.

.asc, .ascii are simple ascii file format for grids, normally generated using the Grid To Ascii tool in ArcGIS, or the GRIDASCII command in ArcInfo Workstation.

.aux is an ancillary file associated with .bil, .tif or other grid (raster) files in ArcGIS.

.avl is an ArcView symbology file used with ArcView 3.x

.dlg the Digital Line Graph format was a legacy ASCII format developed by the USGS in the 1970's and 1980's. Most GIS systems can still import DLG format, but it was largely superseded by SDTS in the 1990's.

.sdts the Spatial Data Transfer Standard is a collection of many files, often stored in a .tar archive. Some GIS systems support SDTS import. Public domain tools are available.

.rdb is a tab-delimited data file conforming to the standards of a legacy set of unix tools for relational database management called RDB. The file format is very simple, consisting of a set of header lines followed by a line of tab-delimited column names, followed by rows of tab-delimited data.

.met, .fgd are FGDC geospatial metadata files in clear-text format. These files document GIS data sets.

Additional Information:

GNU utilities for win32 (includes tar, gzip, gunzip)

Cygwin Unix utilities for win32 (an alternative, more complete Unix environment for Win32)

GeoCommunity Data format descriptions (info about .E00, DLG, SDTS)