Landscape Metrics
Landscape metrics are computed for entire patch mosaic; the resulting landscape output file
contains a single row (observation vector) for the landscape, where the columns (fields) represent
the individual metrics. The first column includes header information about the landscape:
(L1) Landscape ID.--The first field in the landscape output file is landscape ID (LID).
Landscape ID is set to the name of the input image obtained from the input file (see Run
Parameters).
Like class metrics, there are two basic types of metrics at the landscape level: (1) indices of the
composition and spatial configuration of the landscape, and (2) distribution statistics that provide
first- and second-order statistical summaries of the patch metrics for the entire landscape. The
latter are used to summarize the mean, area-weighted mean, median, range, standard deviation,
and coefficient of variation in the patch attributes across all patches in the landscape. Because the
distribution statistics are computed similarly for all landscape metrics, they are described in
common below:
Landscape Distribution Statistics.--Landscape metrics measure the aggregate properties
of the entire patch mosaic. Some landscape metrics go about this by characterizing the aggregate
properties without distinction among the separate patches that comprise the mosaic. These
metrics are defined elsewhere. Another way to quantify the configuration of patches at the
landscape level is to summarize the aggregate distribution of the patch metrics for all patches in
the landscape. In other words, since the landscape represents an aggregation of patches, we can
characterize the landscape by summarizing the patch metrics. There are many possible first- and
second-order statistics that can be used to summarize the patch distribution. FRAGSTATS
computes the following: (1) mean (MN), (2) area-weighted mean (AM), (3) median (MD), (4)
range (RA), (5) standard deviation (SD), and (6) coefficient of variation (CV). FRAGSTATS
computes these distribution statistics for all patch metrics at the landscape level. In the landscape
output file, these metrics are labeled by concatenating the metric acronym with an underscore
and the distribution statistic acronym. For example, patch area (AREA) is summarized at the
class level by each of the distribution statistics and reported in the class output file as follows:
mean patch area (AREA_MN), area-weighted mean patch area (AREA_AM), median patch area
(AREA_MD), range in patch area (AREA_RA), standard deviation in patch area (AREA_SD),
and coefficient of variation in patch area (AREA_CV). Note, the acronyms for the distribution
statistics are the same at the class and landscape levels, so they can only be distinguished by the
output file they belong to (i.e., “.basename”.class or “basename”.land).
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MN (Mean) equals the sum, across all patches
in the landscape, of the corresponding patch
metric values, divided by the total number of
patches. MN is given in the same units as the
corresponding patch metric.
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AM (area-weighted mean) equals the sum,
across all patches in the landscape, of the
corresponding patch metric value multiplied by
the proportional abundance of the patch [i.e.,
patch area (m2) divided by the sum of patch
areas]. Note, the proportional abundance of each
patch is determined from the sum of patch areas
rather than the total landscape area, because the
latter may include internal background area not
associated with any patch.
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MD (median) equals the value of the
corresponding patch metric for the patch
representing the midpoint of the rank order
distribution of patch metric values based on all
patches in the landscape.
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RA (range) equals the value of the
corresponding patch metric for the largest
observed value minus the smallest observed
value (i.e., the difference between the maximum
and minimum observed values) for all patches
in the landscape.
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SD (standard deviation) equals the square root
of the sum of the squared deviations of each
patch metric value from the mean metric value
computed for all patches in the landscape,
divided by the total number of patches; that is,
the root mean squared error (deviation from the
mean) in the corresponding patch metric. Note,
this is the population standard deviation, not the
sample standard deviation.
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CV (coefficient of variation) equals the standard
deviation divided by the mean, multiplied by
100 to convert to a percentage, for the
corresponding patch metric.
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