Methodology and Interpretation
PAGT - Percent total agriculture
The percentage of all agricultural land cover is calculated by dividing the
number of all agricultural land cover (pasture, crops and orchards) cells in the
3 km grid cell reporting unit by the total number cells in the grid cell 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.
Animals grazing in pasture land may decrease vegetation cover possibly leading
to increased runoff. Livestock may also impair stream banks by trampling
riparian vegetation, which may cause increased sedimentation in the stream.
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)