Land Use Primer:
How do scientists measure Land Use and Land Cover and what are some sources of information?
On a small scale, a land use or land cover map can be developed by a team of surveyors. This is not practical at a larger scale.
There are two basic ways to collect the information needed to construct a large-scale land use or land cover map. One way is to use remote sensing. This includes pictures taken by satellites and by airplanes. The information in the pictures is used to determine the land use and land cover for each piece of land. This can involve someone looking at an aerial photo with a magnifying glass, or it can involve computers processing data from hundreds of satellite images.
The United States has two national databases that collect information this way. One is the National Land Cover Database (NLCD) (http://landcover.usgs.gov/nationallandcover.asp
). This database divides up the continental United States into 30 meter by 30 meter squares, and uses data from satellite images to assign each square to a land use/land cover category. This was done nationally using images taken in the early 1990’s. Updated maps using images taken in the early 2000’s are being developed. As of May 2004 the updated maps are available only for part of the Chesapeake Bay drainage area.
The second national land cover database is the National Resources Inventory (NRI) (http://www.nrcs.usda.gov/technical/NRI/). The NRI is a statistical sampling of non-federal land. Prior to 2001, land use and cover were measured every five years at 800,000 sample sites throughout the U.S. using satellite and aerial photos. Beginning in 2001, roughly 200,000 of the sample points are re-done each year, allowing annual updates of trends.
The second way to develop a large-scale land use/land cover map is to determine the land use or land cover for each land parcel. This can be done by surveying land owners. One important large land-owner survey that is conducted every five years is the Census of Agriculture (http://www.nass.usda.gov/census/). The Census of Agriculture surveys every farm in the United States, and asks the operator how much land he or she has in different agricultural uses. A second source of parcel-specific information is your local Tax Assessment Office. In order to assess property taxes for each parcel, the assessor must have information about the parcel’s land use. The assessor’s information will not be sufficient to determine the land's actual use often when the land owner is exempt from paying property taxes. In some cases, your state has parcel-specific information on land use. Many states maintain parcel maps showing national, state and local parks, national and state forests, and agricultural lands. For example, Maryland maintains a state-wide parcel-specific database on land use (http://www.mdp.state.md.us/data/index.htm).
A more complete inventory of data on land use in the Mid-Atlantic Region was prepared for the Mid-Atlantic Integrated Assessment (link: http://www.epa.gov/maia/pdf/landuse.pdf)