Methodology and Interpretation
PURB - Percent urban
The percentage of urban land cover is calculated by dividing the number of
urban land cover cells in the 3 km grid cell reporting unit by the total number
cells in the grid cell boundary minus those cells classified as water (total land area).
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.
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.
Natural Breaks: Classes are based on natural groupings of data values. Natural break points
are identified by looking for groupings and patterns inherent in the data. The features are divided
into classes whose boundaries are set where there are relatively large jumps in the distribution of
* EMAP-West Landscape Metrics Metadata (FGDC)