Quantification of a landscape, or describe landscape in a
meaningful and quantitative way.
Number of Patches ?
Average Patch Size ?
Patch Density ?
Edge Index ?
…
Urban
Wetland
Coniferous Forest
Mixed Forest
What is FRAGSTATS
FRAGSTATS is a spatial pattern analysis program for
categorical maps. The landscape subject to analysis is userdefined and can represent any spatial phenomenon.
FRAGSTATS quantifies the areal extent and spatial
configuration of patches within a landscape. It is incumbent
upon the user to establish a sound basis for defining and
scaling the landscape (including the extent and grain of the
landscape) and the scheme upon which patches are classified
and delineated.
The output from FRAGSTATS is meaningful only if the
landscape mosaic is meaningful relative to the phenomenon
under consideration.
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Questioning before using FRAGSTATS?
• Will the thematic
information meet the
requirements of the project?
• Are the minimum mapping
unit meet the requirements
of the project?
• Where the data come from
and have the data been
validated?
• Is the scale appropriate?
• ……
Digital image classification
Visual interpretation and manual delineation
(USGS Level II)
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A Subset of Land Use and Land Cover Map Near URI
(USGS Level II)
A Subset of Land Use and Land Cover Map Near URI
(USGS Level I)
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Extent is the overall area encompassed by an investigation or
the area included within the landscape boundary. From a
statistical perspective, the spatial extent of an investigation is
the area defining the population we wish to sample.
Grain is the size of the individual units of observation. For
example, a fine-grained map might structure information into
1-ha units, whereas a map with a coarser resolution would have
information structured into 10-ha units.
Extent and grain define the upper and lower
limits of resolution of a study. Any inferences
about scale-dependency in a system are
constrained by the extent and grain of investigation.
FRAGSTATS computes 3 groups of metrics.
• Patch-level – nature of patches, i.e., each patch in the
mosaic (.patch), e.g., average size, size of core area …
• Class-level – nature of each type, i.e., each class (patch
type) in the mosaic (.class), e.g., amount and distribution
of each type
• Landscape-level – nature of the landscape, i.e., the
landscape mosaic as a whole (.land), e.g., pattern,
configuration of entire mosaic, landscape diversity,
heterogeneity
Urban
Coniferous Forest
Wetland
Mixed Forest
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FRAGSTATS also computes the adjacency matrix
(i.e., tally of the number of cell adjacencies between
each pairwise combination of patch types), which is
used in the computation of several class- and
landscape-level metrics.
Landscape Composition
refers to features associated with the variety and abundance of
patch types within the landscape, but without considering the
spatial character, placement, or location of patches within the
mosaic. Because composition requires integration over all patch
types, composition metrics are only applicable at the
landscape-level.
Quantitative measures of
landscape composition: e.g.,
• proportion of the landscape
in each patch type
• patch richness
• patch evenness
• abundance
• patch diversity
Urban
Coniferous Forest
Wetland
Mixed Forest
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Landscape Configuration
refers to the spatial character and arrangement, position, or
orientation of patches within the class or landscape.
•
•
•
•
•
•
Size distribution
Density
Core/edge area
Shape complexity
Isolation/proximity
Dispersion/connectivity
Urban
Coniferous Forest
Wetland
Mixed Forest
Configuration can be quantified in terms of the
landscape unit itself (i.e., the patch).
Shape Index
• Complexity of the patch shape relative to a square of
the same size
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Isolation/Proximity
• Spatial context of patches (rather than the patches themselves)
Contagion
• Landscape texture
• Tendency for cell types to be spatially aggregated,
dispersed
• Are cells of similar patches aggregated?
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Connectivity
• Degree to which a landscape facilitates or impedes flow
• How connected is a particular type/class?
Scale Consideration
FRAGSTATS does not limit the scale (extent or grain) of
the landscape subject to analysis.
The distance- and area-based metrics are reported in
meters and hectares, respectively.
FRAGSTATS outputs data files in ASCII format that can
be manipulated using database management programs to
rescale metrics or to convert them to other units.
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FRAGSTATS Metrics
The area (AREA) of each patch is an
important and useful piece of
information contained in the
landscape.
However, the size of a patch may not
be as important as the extensiveness
of the patch for some organisms and
processes.
FRAGSTATS Metrics
Class area (CA) and percentage of landscape (PLAND) are
measures of landscape composition; specifically, how much of
the landscape is comprised of a particular patch type.
This is an important characteristic in a number of ecological
applications. For example, how much of the target patch type
(habitat) exists within the landscape in association with
habitat requirements (fragmentation, isolation, minimum area,
etc.)?
In addition to its direct interpretive value, class area is used in
the computations for many of the class and landscape metrics.
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FRAGSTATS Metrics
Radius of gyration (GYRATE) is a
measure of patch extent; that is,
how far across the landscape a
patch extends its reach.
All other things equal, the larger
the patch, the larger the radius of
gyration. Similarly, holding area
constant, the more extensive the
patch (i.e., elongated and less
compact), the greater the radius of
gyration.
FRAGSTATS Metrics
The radius of gyration can be
considered a measure of the average
distance an organism can move within a
patch before encountering the patch
boundary from a random starting point.
When aggregated at the class or
landscape level, radius of gyration
provides a measure of landscape
connectivity (known as correlation
length) that represents the average
traversability of the landscape for an
organism that is confined to remain
within a single patch.
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FRAGSTATS Metrics
Number of patches (NP) or patch density (PD) of a particular
habitat type may affect a variety of ecological processes,
depending on the landscape context.
For example: Those may
• determine the number of subpopulations in a spatially-dispersed
population for species exclusively associated with that habitat type;
• alter the stability of species interactions and opportunities for coexistence
in both predator-prey and competitive systems;
• can serve as general indices of spatial heterogeneity of the landscape
mosaic
• …
Number or density of patches is probably most valuable as the
basis for computing other more interpretable metrics.
FRAGSTATS Metrics
Reduction in the size of habitat
fragments is a key component of
habitat fragmentation.
A landscape with a smaller mean
patch size for the target patch type
than another landscape might be
considered more fragmented.
Thus, mean patch size can serve
as a habitat fragmentation index.
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FRAGSTATS Metrics
Mean patch size at the class level is a function of the number of
patches in the class and total class area. In contrast, patch
density is a function of total landscape area. Therefore, at the
class level, these two indices represent slightly different aspects
of class structure. For example, two landscapes could have the
same number and size distribution of patches for a given class
and thus have the same mean patch size.
If total landscape area differed, patch density could be very
different between landscapes.
FRAGSTATS Metrics
Alternatively, two landscapes could have the same number of
patches and total landscape area and thus have the same patch
density.
If class area differed, mean patch size could be very different
between landscapes. These differences should be kept in mind
when selecting class metrics for a particular application.
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FRAGSTATS Metrics
FRAGSTATS computes several
statistics representing the amount of
perimeter (or edge) at the patch, class,
and landscape levels.
Edge metrics usually are best
considered as representing landscape
configuration, even though they are not
spatially explicit.
FRAGSTATS Metrics
At the patch level, edge is a function
of patch perimeter (PERIM).
At the class and landscape levels,
Total edge (TE) is an absolute measure of total edge length of a
particular patch type (class level) or of all patch types (landscape
level).
Edge density (ED) standardizes edge to a per unit area basis that
facilitates comparisons among landscapes of varying size.
However, when comparing classes or landscapes of identical
size, total edge and edge density are completely redundant.
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FRAGSTATS Metrics
Landscape shape index (LSI) measures the perimeter-to-area
ratio for the landscape as a whole.
LSI is identical to the shape index at the patch level (SHAPE),
except that it is based on class area and the associated class
perimeter at the class level and the total landscape area and all
edges at the landscape level.
FRAGSTATS also computes a normalized landscape shape
index (nLSI) in which the metric is rescaled by the minimum
and maximum values.
Limitations of FRAGSTATS Metrics
All edge indices are affected by the resolution of source images
for mapping. Generally, the finer the resolution, the greater the
edge length. At coarse resolutions, edges may appear as
relatively straight lines; whereas, at finer resolutions, edges
may appear as highly convoluted lines. Values calculated for
edge metrics should not be compared among images with
different resolutions.
30-meter Spatial Resolution
2-meter Spatial Resolution
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Limitations of FRAGSTATS Metrics
Patch perimeter and the length of edges
will be biased in raster images because
of the stair-step patch outline, i.e. the
measured edge length is always more
than the true edge length. This will
affect all edge indices.
The magnitude of this bias will vary in
relation to the grain or resolution of the
image. The consequences of this bias
with regards to the interpretation and
use of these indices must be weighed
relative to the phenomenon under
investigation.
Check FRAGSTATS documentations and HELP files
for more details on:
•
•
•
•
•
•
•
•
Shape Metrics
Core Area Metrics
Isolation/Proximity Metrics
Contrast Metrics
Contagion/Interspersion Metrics
Connectivity Metrics
Diversity Metrics
……
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Output Files
Depending on which metrics are selected by the user,
FRAGSTATS creates 4 output files corresponding to the three
levels of metrics and the adjacency matrix. The user supplies a
"basename" for the output files and FRAGSTATS appends the
extensions .patch, .class, .land and .adj to the basename. These
files are formatted to facilitate input into spreadsheets and
database management programs:
Output Files
• "basename".patch file.–Contains the patch metrics; the file
contains 1 record (row) for each patch in the landscape; columns
represent the selected patch metrics.
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Output Files
• "basename".patch file.–Contains the patch metrics; the file
contains 1 record (row) for each patch in the landscape; columns
represent the selected patch metrics.
CSD = Standard Deviations from the Class Mean
CPS = Percentile of the Class Distribution
LSP = Percentile of the Landscape Distribution
LPS = Landscape level percentile
PERIM = Patch Perimeter
PERM_CSD = Patch perimeter standard deviation
Output Files
"basename".class file.–Contains the class metrics; the file
contains 1 record (row) for each class in the landscape; columns
represent the selected class metrics.
CA = Total (Class) Area
PLAND = Percentage of Landscape
LPI = Largest Patch Index
TE = Total Edge
AREA_MN = Area Mean
AREA_AM = Area weighted mean
AREA_MD = Area Median
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Output Files
"basename".land file.–Contains the landscape metrics; the file
contains 1 record (row) for the landscape; columns represent the
selected landscape metrics.
TA = Total Area
LPI = Largest Patch Index
TE = Total Edge
ED = Edge Density
AREA_MN = Area Mean
AREA_AM = Area weighted mean
AREA_MD = Area Median
AREA_RA = Area Range
AREA_SD = Area standard deviation
Output Files
“basename”.adj file.–Contains the class adjacency matrix; the
file contains a simple header in addition to 1 record (row) for
each class in the landscape, and is given in the form of a 2-way
matrix. Specifically, first record contains the input file name,
including the full path. The second record and first column
contain the class IDs (i.e., the grid integer values associated with
each class), and the elements of the matrix are the tallies of cell
adjacencies for each pairwise combination of classes.
ID
3
1
4
2
3
3436
223
1243
260
1
223
1652
160
26
4
1243
160
5506
155
2
260
26
155
566
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