Methodology and Interpretation
PAGC - Percent cropland
The percentage of cropland cover is calculated by dividing the number of
cropland 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).
Agricultural practices typically employ fertilizers, pesticides and other chemicals
that may be transported to streams in water runoff. The closer agriculture is to a
stream the more likely related pollutants will enter the stream. Concentrations of
pollutants transported into streams are also more likely to be higher when
agriculture is closer to streams.
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)