Online Worldwide Spatial Data

ASTER Global Digital Elevation Model: 30m Resolution

• ASTER FTP
• ASTER GDEM
• Warehouse Inventory Search Tool (WIST)
• More about this dataset

Shuttle Radar Topography Mission (SRTM): 30m in US, 90m Outside

• Seamless
• CGIAR Consortium for Spatial Information (CGIAR-CSI)
• More about this dataset

Other Data Sources

• Center for Satellite Based Crisis Information: Presents a service of the German Remote Sensing Data Center (DFD) of DLR. It provides a 24/7 service for the rapid provision, processing, and analysis of satellite imagery during natural and environmental disasters for humanitarian relief activities and civil security issues worldwide. The resulting satellite-based information products are provided to relief organisations and public authorities and are also freely available on the ZKI website.
• OpenStreetMap: Creates and provides free geographic data such as street maps to anyone who wants them. The project was started because most maps you think of as free actually have legal or technical restrictions on their use, holding back people from using them in creative, productive, or unexpected ways. Download data in different formats from Cloudmade.
• GeoCommons: Finder! lets one search for data, upload, download, and convert between SHP, CSV, and KML. Maker! enables one to make maps on the web.
• DIVA-GIS: Free spatial data for countries around the world
• GTOPO30 & Hydro1k: A free global digital elevation model (DEM) with a horizontal grid spacing of 30 arcseconds (approx. 1 k). HYDRO1k is a geographic database developed to provide comprehensive and consistent global coverage of topographically derived data sets, including streams, drainage basins, and ancillary layers derived from the USGS' 30-arcsecond DEM of the world (GTOPO30).
• Global Land Cover Facility (GLCF): "...the best open source for Landsat TM and Landsat ETM on the planet..." - Digital Terrain Modeling and Mapping Journal. In addition to Landsat imagery, GLCF hosts MODIS, AVHRR, and more.
• United Nations Environmental Program: Holds more than 400 different variables, as national, subregional, regional, and global statistics or as geospatial datasets (maps) covering themes like fresh water, population, forests, emissions, climate, disasters, health and GDP.
• European Environment Agency Interactive Maps and Data
• Landsat: An affiliate of the Tropical Rain Forest Information Center (TRFIC). Now hosts the Global Orthorectified Landsat Datasets for three epochs for free download: 1970's MSS, 1990's TM, and 2000's ETM+.
• NGA GEOnet Names Server (GNS)
• NOAA Surface Inventories and Station Lists: Hourly climate data can be found in the integrated surface hourly database inventory
• Center for International Earth Science Information Network
• Geoscience Data Link: Hosted by the Lamont-Doherty Earth Observatory. Visitors can search by data types, date, and regions. Includes information on marine, continental and polar environments. Includes a global bathymetry database, which allows users to look at maps and download grids.
• NCAR Scientific Support Section: A large number of datasets (some free and some for a fee) from the National Center for Atmospheric Research.
• USGS Eros Data Center
• Digital Chart of the World Web Server: An ESRI product originally developed for the US Defense Mapping Agency (DMA) using DMA data.
• Harvard Geospatial Library: Provides an online tool for locating data around the world. Dated located on their web site includes Digital Chart of the World, Census 2000 Block Groups and Tracts, ESRI Data & Maps (6 CDs), MassGIS vector data, municipal data for Boston, Cambridge, and Brookline, and the National Transportation Atlas.
• National Geophysical Data Center: A general site for geophysical data. Datasets are not necessarily in GIS-ready formats.
• The Center for Advanced Spatial Technologies (CAST): A great site to start searching for data. The site includes a listing of data by 28 different subject areas including; crime, census, health, remote sensing, and much more. It also has a great listing of national and international GIS data catalogs. One of the best features includes a listing of US State GIS data centers.
• Map Digger: Has an interesting listing of weather, road, nautical, historical, and aviation maps.
• GIS Data Depot
• The GeoCommunity Data Store: For purchase data bundles
• Geo-Referencing of Ethnic Groups: Polygons to represent ethnic groups around the world
• World Wildlife Fund (WWF): Ecoregions of the world, hydrology, wetlands, etc.