Methodology and Interpretation

Land-Cover Percent Urban Change
The percentage of urban land-cover is calculated (in each of the following time periods: early 1970s, 1980s, 1990s, and 2003) by dividing the number of urban land-cover cells in the reporting unit by the total number of land-cover cells in the reporting unit minus those cells classified as water (i.e., total land area). Because 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, change in this metric may indicate an increase, decrease, or no change in these ecological services over time, among reporting units.

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

• 1970s Land-Cover - Metadata

• 2003 Land-Cover - Metadata