The US Geological Survey (USGS) performs a wide variety of tasks related to the environment including data acquisition for use in geographical information systems. This data set provides elevation data for the contiguous US, Hawaii, and Alaska. Data are in one-by-one degree blocks and available via an online interface or by ftp download (instructions provided in the User Guide). Specific data can...

With the release of such programs as Google Earth, computer users have access to a rather diverse set of geographical data tools. One program that has recently been released in a new edition is the Geographic Resources Analysis Support System (GRASS). With this program, users can perform a number of tasks, such as spatial modeling, visualization, and image processing. The program may be a bit...

QGIS is a cross-platform desktop geographic information system that allows users to "create, edit, visualize, analyze, and publish geospatial information." In addition to functioning as a complete, standalone GIS system, QGIS can also be integrated with other open source GIS software, including PostGIS, GRASS, and MapServer. Plugins that extend QGIS can be written in the Python or C++ programming...