Methodology and Interpretation

Percent urban within 120 meters of wetlands
The affect of runoff from areas adjacent to wetlands may be strongly influenced by land cover type that occupies a zone (i.e., a buffer zone), up to approximately 120 meters from the edge of a wetland. Thus, the percentage of urban land cover within 120 meters of wetlands is calculated by summing the total number of urban land cover cells within a four cell buffer (120 meters) zone on the perimeter of wetland patches in the reporting unit and dividing by the area of the buffer plus the area of the buffered wetland. Cells outside buffer zones for wetlands within each reporting unit are ignored. Other buffer distances may be more appropriate, depending on the runoff chemical constituent(s), flow dynamics, soil conditions, position of wetland in the landscape, and other landscape characteristics.

Quantile: Each class contains an approximately equal number (count) of features. A quantile classification is well-suited to linearly distributed data. Because features are grouped by the number within each class, the resulting map can be misleading, in that similar features can be separated into adjacent classes, or features with widely different values can be lumped into the same class. This distortion can be minimized by increasing the number of classes.

Metric input GIS data:

• United States Hydrologic Units (8-digit HUCs) - Metadata

• United States Coastal Change Analysis Program (CCAP) - Metadata