While GIS software itself is the engine of digital spatial analysis, the fuel is data about the places your land trust works to protect. Here are starting sites for GIS data that most land trusts need to do effective mapping.

Major Web Portals for Data

US Geological Survey - The USGS National Map web site is a great resource for a wide range of data and information about data (metadata). Basic geographic data is available from the USGS web site and other vendors (this data includes Digital Raster Graphic files (DRGs, the standard USGS “topo” quads), Digital Elevation Models (DEMs, used to create shaded relief mapping, etc.), Digital Line Graphs (DLGs, the individual elements of topo quads), and Digital Ortho Quads (DOQs, aerial imagery).

Also as of January 2007, all USGS air photographs (black and white Digital Othro Quads) are available for free Internet download at the Internet Archive web site.

Finding USGS quads - Need to find a USGS quad map?  Topozone and USGSquads.com allow onscreen viewing of the map you are looking for along with other useful information (coordinates, map ordering, data purchase, etc.).  You can also get GIS data of quad map boundaries.

CAST - Center for Advanced Spatial Technology (Univ. Arkansas)   An excellent portal to data for each state, particularly natural resources information.

GIS DataDepot - the most comprehensive overall commercial site for USGS and other GIS data. Very easy to do online purchases.

U.S. Government Geospatial Data portal – a consolidated framework for all U.S. government GIS data, very useful and powerful framework for natural resource information, as well as pollution and demographic data.

U.S. Bureau of the Census – the Census bureau not only has huge stores of demographic information (quick online access at American Factfinder), but it also maintains the TIGER data set which has state, county, city and census boundary files, along with roads, streams and much more.  A commercial service that sells bundled data from TIGER and the Census is CensusCD – these products cost several hundred dollars for a state, but save much time integrating different data sets for GIS use.

Conservation Geoportal The Conservation Geoportal is a collaborative effort by and for the conservation community to facilitate the discovery and publishing of geographic information systems (GIS) data and maps, to support conservation decisionmaking and education. It is primarily a data catalog, intended to provide a comprehensive listing of GIS data sets and map services relevant to biodiversity conservation.  The Conservation Geoportal does not actually store maps and data, but rather the descriptions and links to those resources, known as "metadata."

Advanced Data and Sources

For more experienced GIS users, the following sites have very useful data, services or links to more data:

Natural resources data:  There are huge numbers of sites that have natural resources data. The USGS and CAST sites  noted above are always good starting points, but also try these:

•  The Nature Conservancy GIS data site
  

• Land cover data: Multi-Resolution Land Characteristics Consortium (MLRC)
  
• Habitat (GAP) data:  National GAP headquarters
  
• Rivers and streams data:  National Hydrography Dataset
  

Aerial imagery/remote sensing data:  The sites below have aerial images that you can purchase or download for free and bring into your GIS as raster data (basically a photo that underlays your other GIS data).  Most are created from satellite images, some from airplane-based photography. Imagery that is 1 meter/3 foot resolution (each pixel is 1 meter on a side) is very good (2' or 1' is extremely good) - imagery that is 10 meter is only good for overall landscape images, usually not for site mapping. Generally the more resolution, the higher the cost.  Natural color imagery is best for general work, but black and white can work if color not available.  False color, infrared and other non-natural color imagery is usually better for expert users.  Imagery that allows you to analyze  its colors  (or bands), is more expensive and takes special software and skills  (links to ERDAS and ESRI Image Analysis).

• US Dept. of Agriculture NAIP:   The National Agricultural Inventory Program has prepared state-wide data sets of 1 meter color aerial imagery for many states, often available by county for free download. This is very good data and a bargain for land trusts!
  
• TerraServer - This is a USGS/Microsoft site that you can use to examine black and white Digital Ortho Quad images (DOQs) and color Digital Raster Graphics (DRGs – pictures of standard USGS topo maps) anywhere in the U.S.
• Airphoto USA - provides high resolution color imagery in much of the U.S. Imagery older than 2-3 years can often be gotten for a substantial discount. Works well with ESRI GIS software.
  
• Other satellite data - There are many sources of such data, Directions Magazine has a useful catalog of such vendors .
  

Geocoding data/services:   Geocoding is matching places to their geographic coordinates. Most geocoding is done with point data (e.g., giving coordinates to a list of people or sites) based on street addresses, then the data is imported into a GIS project. Most GIS software can geocode, but rates of accuracy are increased when better street data (and better geocoding software) is used.  U.S. Census TIGER streets are adequate for basic geocoding but commercial data (see www.teleatlas.com) will often improve the number of features that are given coordinates - at a cost, of course.

Batchgeocode.com, a free online geocoding service, is available and allows you to copy and paste from a spreadsheet or database a whole group of addresses into a web window (up to 50,000 records at a time). The service will then give each data point a latitude/longitude value and an accuracy score.  You can get more detailed and robust geocoding services and information at the Univ. So. Calif. WebGIS site.

If you cannot find what you want from the above, type the following in an Internet search page:   GIS data [subject words] [state/location words]. You can add "download" or "price" to the query to return those options.

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