Several important measurements on the landscape such as area of selected land cover classes, percent of a watershed in impervious surfaces, and adjacent land use can often be reliably determined from remotely sensed data. The capabilities and utility of such data have greatly expanded in the last several years, and the cost has been reduced. A section of the "Guidelines for Mapping Vegetation on Army Installations" (O’Neil and Hill 2000) introduces and defines sources of remotely sensed data (aerial photography and digital imagery). Campbell and Graves (2000) is excerpted from the Guidelines, slightly modified, and reproduced here. Included are data features and aspects of planning for information collection, such as costs and input to contractor specifications.
One valuable source of information is the National Gap Analysis Program (http://www.gap.uidaho.edu/) whose mission is "to provide regional assessments of the conservation status of native vertebrate species and natural land cover types and to facilitate the application of this information to land management activities." This is a nation-wide effort being conducted at the state level. The page http://www.gap.uidaho.edu/Tools/ contains a link to the Gap Handbook with numerous sections on spatial data, including access of Landsat Thematic Mapper (TM) satellite images to generate a digital base. In the Gap program, air photos, air video, other maps, and field observations are used to interpret and refine the TM-derived spatial data. Information on how to access Gap products can be found at http://www.gap.uidaho.edu/Projects/Data.asp. A full description of the Program is available at: http://www.gap.uidaho.edu/About/Overview/GapDescription/default.htm#Goals_and_Objectives.
Another good source is the U.S. Geologic Survey, who supplies data on land use and land cover (LULC) that describe vegetation, water, natural surface, and cultural features on the land surface. Data obtained over the Internet are available at no cost. Anderson et al. (1976) is the basis for classification, with results based on manual interpretation of aerial photography. Databases are available at twoscales (1:250,000 and 1:100,000). Coverage exists for most of the contiguous states and Hawaii. Background and ordering information for LULC can be found at: http://edcwww.cr.usgs.gov/glis/hyper/guide/1_250_lulc.