Spatial Information Resources 

GIS Data Depot
"Numerous data holdings available for free download" from The GeoCommunity™

ESRI's Geography Network
Many downloadable data layers are available online. Data can be accessed interactively when using ArcView 9.x by using the Get Data --> Geography Network path.

Harvard Geospatial Library

Stanford University's webpage for digital GIS data.

National & International GIS data
From the University of Arkansas libraries, a country list of GIS data sources.

GeoData.gov U.S. Maps and Data
"Your one stop for Federal, state, and local geographic data." Includes feature topics (i.e., Fire Mapping) and a map viewer.

National Spatial Data Clearinghouse
Searchable collection of over 250 spatial data servers, that have digital geographic data primarily for use in Geographic Information Systems.

USGS Earth Resources Observation & Science (EROS)
"A leading source of land information for exploring our changing planet."

GIS Data Finder
From UNC Chapel Hill, "a large collection of data sets, each of which is made up of potentially many individual data layers. The GIS Data Finder allows our patrons to browse our collection in several ways."

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GIS Data Depot
"Numerous data holdings available for free download" from The GeoCommunity™

ESRI's Geography Network
Many downloadable data layers are available online. Data can be accessed interactively when using ArcView 9.x by using the Get Data --> Geography Network path.

Data.gov
A great source of shapefiles from federal sources. Use the data.gov and geodata tabs to search for spatial datasets, then drag them into the text box at the top to preview them in a map viewer.

NationalAtlas.gov
A Raw Data ftp site of a wide variety of national data layers.

EPA National Geospatial Program
These web services show facilities regulated by EPA. They can be loaded into a map interface by accessing http://geodata.epa.gov and loading one of the 10 available services. Viewing these image and feature services along with local data can be done in ArcMap.
Includes: Air Emissions; National Priority List; Toxic Release Inventory; and more.

NGA Geospatial Engine
Raster data searchable by map and by name.

Global Land Cover Facility
"The GLCF develops and distributes remotely sensed satellite data and products that explain land cover from the local to global scales, available free to anyone via FTP."

SEDAC: Socioeconomic Data & Applications Center
From Columbia University, a collection of data sources, often GIS-friendly.

Map Library
Free map data & software, with Africa data currently offered. May require some assistance for use with ArcGIS. See GIS librarian for details.

Mexican Topographic Map Guide
A for-fee service that offers .shp and .drg files of Mexico maps.

World Data Center for Human Actions in the Environment. "This portal, hosted by NASA’s Socioeconomic Data and Applications Center (SEDAC), provides access to a wide range of global data, associated documentation, and visualization and analysis tools, and to the community of experts on global data."

United Nations Environment Programme Geo Data Portal
An online database of UNEP datasets containing more than 450 variables.

Center for International Earth Science Information Network Downloadable Data page
From Columbia University, a great source of international and domestic free data.

The Southern Africa Human-development Information Management System (SAHIMS) GIS Library
A wealth of free GIS data for many African countries.