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Methodology and Interpretation
RNAT30 - Percent all natural land use within 30 meters of streams
The percentage of natural land cover 30 meters adjacent to streams is
calculated by summing the total number of forest, shrub land, grassland,
wetland, and bare rock land cover cells underneath stream segments in the
3 km grid cell reporting unit and within a one cell buffer (30 meters) and
dividing by the stream corridor's total land area (all cells 30 meters
adjacent to streams minus those classified as water). Cells inside the buffer
zone but outside of the grid cell boundary are ignored. High amounts of intact
natural cover near streams may provide a barrier to some pollutants that would
otherwise enter the stream. Forests and wetlands are particularly effective at
filtering nutrients and other chemicals from runoff.
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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