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Methodology and Interpretation
PFPERF9 - Percent 3 km grid cell defined as perforated forest
Percent perforated forest is calculated using a moving 270 meter square
window (9 pixels x 9 pixels) across the land cover. When the percent forest in
the window is greater than 60%, and greater than the window's PFF9 value, the
forest cell in the center of the window is categorized as perforated. The number
of perforated forest cells in the 3 km grid cell reporting unit is then divided
by the grid cell's total land area (the total number cells in the grid cell boundary
minus those cells classified as water) to derive PFPERF9. A perforated designation
indicates largely continuous forest, and non-forest land cover is clumped. Perforated
forest probably provides migration corridors across an area, but may or may not
provide suitable interior habitat, depending on the species.
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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