This section was prepared by Michael R. Waring, Vicksburg, MS.
Many different ways to classify land cover types have been developed at the national, state, and regional levels. Systems in use are based on various characteristics that range from objective to subjective. Some of the more popular systems are based on land use or type, morphology, capability, life forms, combinations (e.g., ecoregions, soil, vegetation, hydrogeomorphic features), values, and objectives.
Given the large number of classification systems that have been developed, it is often difficult to decide which is most appropriate for a particular situation. When selecting a classification system, it is important to remember that:
1. The classification system should serve the objectives and scale of the problem and landscape.
2. Those systems based on objective characteristics are more defensible and can be more consistently applied than those based on subjective characteristics.
3. If values are included as part of the system, that should be made clear so that if values change, the classification can be adjusted.
4. Where multiple classification systems may be applicable for a project, one that uses FGDC standards should be selected; or if not selected, the user must be able to "cross-walk" the new system to FGDC standards. As an example of cross-walking, see the table below courtesy of Steve Eggers, St. Paul District. Column 1 shows the names of cover types used to easily communicate with all interested parties for a project in the upper Midwest. Column two gives the Cowardin et al. (1979) classes that correspond to column one. For cross-walking in map preparation, please consult with appropriate GIS and remote sensing personnel to assure that mapping standards are met.
The following matrix was developed to aid in selecting a classification system, and addresses the currently recognized and accepted national classification systems. Systems were selected to provide the reader with a variety of options to consider. While national in the scope of development, actual application will be at the regional or local level. Care should be taken when adapting or applying a particular classification method across multiple regions, or to regions that differ significantly from those defined in the classification (e.g., a particular watershed or a Corps Division).
The questions along the left side of the matrix are typical of those that might be asked when selecting a classification system. The assignment of the various classification systems to a particular cell in the matrix represents a broad-brush approach that attempts to show the strength of the classification. This does not limit the user from altering a system to meet a specific need, e.g., adding modifiers to Cowardin et al. (1979), subdividing forest cover types (Society of American Foresters 1980) by stage of succession, or aggregating the National Vegetation Classification Standards to the physiognomic classes for application at the landscape level.
To view the matrix in its entirety, click here.
At what level are you working?
¹ For Corps Divisions, an "X" in the first row indicates the classification system is applicable throughout the Corps. "Watersheds" are considered typically to be a single drainage system, whereas "Local" will be a subset of the watershed. At the Division and Watershed levels, the classification systems can generally be used with existing data sets. Local classifications may require field work to obtain appropriate data.
What system(s) are you most concerned with?
² Most of the classification systems can be aggregated to a landscape level for application to a Division or watershed, but not all can be disaggregated to a local level. For example, a classification system such as Bailey’s Ecoregions can best be applied over a broad area, such as a Corps District or watershed, whereas Cowardin’s system can be applied not only at the largest scale but also on a local basis.
³ As presented in Corwardin et al. (1979)
Augmented by Johnson et al. (1984)
What elements within the system are you most interested in assessing?
What is the activity or function for which the assessment is needed?
Which methods follow Federal data standards?
