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Methodology and Interpretation
RAGT120 - Percent total agricultural within 120 meters of streams
The percentage of all agricultural land cover 120 meters adjacent to streams
is calculated by summing the total number of pasture, crop and orchard 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. 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
data values.
* EMAP-West Landscape Metrics Metadata (FGDC)
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