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Land Cover Analysis
Appropriate Use FAQs
Note that glossary terms on this page will be followed
by a Why are watersheds important?Watersheds Even if you do not live on the coast, you may still impact the quality of the water. For example, the Chesapeake Bay's watershed covers over 64,000 square miles of land and includes the District of Columbia and parts of New York, Pennsylvania, Delaware, Maryland, Virginia, and West Virginia. Anything that enters the water system upstream must move downstream and eventually into lakes and the ocean, where it collects. As humans consume resources from these aquatic habitats, such as fish, they become the final recipients of their own pollution. For more information about watersheds and pollution see the "Chesapeake Bay Foundation: State of the Bay" Web site. Satellite imagery and geographic information systems (GIS) provide tools to monitor the status and condition of the landscape. For instance, science-based analysis has identified direct links between the amount of impervious surface in a watershed and the water quality. Once a threshold of impervious surface is reached, water quality decreases proportionally. For more information on applications involving impervious surface analysis, see the Nonpoint Education for Municipal Officials Project (NEMO). Can I use a satellite-derived image the same as other data sources (i.e., aerial photographs, DOQ)?Satellite imagery and aerial photography are in many ways complementary. They both have their strengths and weaknesses. Satellite imagery is useful because of its stable nature (same resolution, same time, same data characteristics). Aerial photography is useful because of its customizable nature (flexible time, flexible resolution, flexible data characteristics). Some analyses can be conducted in the same manner with both data sets. Aerial photography can be used for detailed species mapping because of its ability to collect high-resolution information. However, there are many applications that are more appropriate from satellite imagery, such as land cover mapping and change detection analysis. Once the remotely sensed imagery has been processed into derived products, such as land cover, the data products can be used in the same way as derived data sets from other image sources. They can certainly be used together to answer questions regardless of the origin. How can I tell if C-CAP data are appropriate for my needs?C-CAP data are mapped at 1:100,000 scale with 22 standard classes constituting major landscape components. They are not jurisdictional (can't be used for permitting) and will not identify individual species. However, they are useful for identifying regional landscape patterns and major functional niches (habitat), and for environmental impact assessment, urban planning, and zoning applications. C-CAP also provides a "change" data set so that users can see how the landscape is changing over time. If I overlay the C-CAP data with a DOQ, I see areas in the C-CAP that appear to be classified incorrectly. Why?C-CAP data are developed from Landsat Thematic Mapper (TM) digital satellite imagery. These images have a base scale of 1:100,000 for mapping applications. This scale of mapping means that the data should be within 60 meters of the exact location on the Earth 90 percent of the time according to U.S. Geological Survey (USGS) National Mapping Accuracy Standards. There are numerous sources of spatial error that can account for shifts in the data against their exact position on the Earth. It is important to remember that C-CAP data maintain accuracies of 85 percent as a general rule. Some land cover classes will be higher, some lower. Within these data sets, 85 percent accuracy also means 15 percent inaccuracy. There certainly will be errors, but C-CAP has taken logical steps to minimize errors and has done extensive fieldwork to eliminate them. Can I use C-CAP data to locate specific species, such as an endangered species of tree?Because of the base scale of Landsat Thematic Mapper (TM) data, C-CAP data are not appropriate for identifying specific species. However, they are useful for identifying appropriate habitat on a regional scale. C-CAP data can be used to evaluate potential habitat if identifying characteristics are available, such as species X needs Y acres of forested space within 500 meters of a water body. Can I use the C-CAP data for permitting purposes, such as docks or development near wetlands?Permitting cannot be accomplished from data at scales of 1:100,000. It would be more appropriate to use data at scales of 1:12,000 and higher. Therefore, C-CAP data are not appropriate for permitting applications. However, C-CAP data could be used for zoning applications and used to identify resources and wetlands for conservation, preservation, and proper zoning decisions. Can I use C-CAP data for legal monitoring of wetlands?C-CAP data sets are not for use in litigation. While efforts have been made to ensure that these data are accurate and reliable within the limits of current technology, the National Oceanic and Atmospheric Administration (NOAA) cannot assume liability for any damages, or misrepresentations, caused by any inaccuracies in the data, or as a result of the data to be used on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty. |
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