Methodology and Interpretation
PCTIA_RD - Percent total impervious area based on road density
The percent total impervious area is calculated using road density as
the independent variable in a linear regression model (May et al. 1997).
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.sss
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)