Methodology and Interpretation

Percent urban within 120 meters of streams
The percentage of urban land-cover within 120 meters of a stream is calculated by summing the total number of urban land-cover cells underneath stream segments in the reporting unit and within a four cell buffer (120 meters) and dividing by the stream corridor's total land area (i.e., all cells within 120 meters of streams minus those classified as water). Cells inside the buffer zone but outside of the reporting unit boundary are ignored. High amounts of urban land indicate substantial modification of natural vegetation cover and may have profound effects on wildlife habitat, soil erosion and water quality. The closer urban land is to a stream the more likely it will have adverse affects on the stream habitat and water-quality.

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. For continuity of the browser content, and consistency among maps, legend gradients are from higher values (red) to lower values (green).

Metric input GIS data:

• 244 Subwatersheds - Metadata

• 2003 Land-Cover - Metadata

• Stream Network - Metadata