Methodology and Interpretation

Percent Impervious Surfaces
The percent total impervious area is calculated using road density as the independent variable in a linear regression model, as described in:
May, C.W., Horner, R.R., Karr, J.R., Mar B.W., Welch, E.B. 1997. Effects of urbanization on small streams in the Puget Sound Lowland Ecoregion. Watershed Protection Techniques. 2:4. pp. 483-493.

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

• Road Network - Metadata