Methodology and Interpretation

RAGC120 - Percent cropland within 120 meters of streams
The percentage of cropland cover within 120 meters of a stream is calculated by summing the total number of cropland land cover cells underneath stream segments in the 3 km grid cell reporting unit and within a three cell buffer (120 meters) and dividing by the stream corridor's total land area (all cells 120 meters adjacent to streams minus those classified as water). Cells inside the buffer zone but outside of the grid cell boundary are ignored. 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 data values.

* EMAP-West Landscape Metrics Metadata (FGDC)