Figure 5. Patch metrics dialog box depicting the Area/Perimeter metrics tab. Each tab
corresponds to a different suite of metrics.
Step 3. Selecting and Parameterizing Patch, Class, and Landscape Metrics
The next step is to select and parameterize the patch, class, and landscape metrics. Note, these options are available only if you select the respective output statistics in the Run Parameters dialog box. By the selecting the select patch metrics option in the Fragstats drop-down menu, the Patch Metrics dialog box will display (Fig. 5). Similarly, by selecting the select class metrics or select landscape metrics options, the corresponding dialog boxes will display. Each dialog box consists of a series of tabbed pages. Each tabbed page represents a group of related metrics. The organization of these metric groups is discussed in the Background Material documentation.
Figure 5. Patch metrics dialog box depicting the Area/Perimeter metrics tab. Each tab
corresponds to a different suite of metrics.
The selection of metrics is relatively straightforward. On each tabbed page select the desired individual metrics using the check boxes, or select all of the metrics using the Select All button. If you select all the metrics, the button function will change to a Clear All function. Clicking on the button now will deselect all metrics. Each metric is discussed in detail in the FRAGSTATS Metrics documentation.
A number of metrics require you to provide additional parameters before they can be calculated. In some cases this involves simply selecting among the alternatives provided (e.g., by clicking on a radio button), in other cases this involves entering a number in a text box, and in still other cases, this involves specifying a separate user-supplied filed. These special requirements are described below in association with the corresponding tabbed page.
1. Area/Density/Edge Metrics.–If you select TOTAL EDGE or EDGE DENSITY on the Area/Density/Edge Metrics tab at either the class or landscape level, you must specify how you want to treat boundary and background edges (Fig. 6); specifically, what proportion of the landscape boundary and background class edges to treat as true edge and therefore included in the edge length calculations? Note, if a border is present, then only background edges are affected by this designation, since all other edges along the landscape boundary will be made explicit by the information in the border. If a border is absent, then all boundary and background edges are affected. See the Overview section for a more detailed discussion. There are three options:
(1) None.–Do not count any boundary/background as edge.
(2) All.–Count all boundary/background as edge.
(3) Partial.–Specify the proportion of boundary/background edge to treat as an edge (weight = fraction between 0 and 1). For example, if you specify .5, then half the total length of edge of involving the landscape boundary (if a border is absent) and any internal background will be included as edge in the affected metrics.
Figure 6. Class metrics dialog box with the Area/Density/Edge tab showing.
The radio buttons associated with background/boundary are active it either
Total Edge or Edge Density are checked.
2. Core Area Metrics.–If you select any core area metric at the patch, class, or landscape level, you must specify the depth-of-edge to use in determining what constitutes the core of a patch. There are two options:
(1) Enter constant edge depth.–If you wish to treat all edges the same, then check the corresponding check box and enter a non-zero distance (in meters). By default this box contains a zero, but you must enter a non-zero distance before closing the dialog box or you will receive an error message in the log window. Note, a zero depth-of-edge would result in the core area being equal to patch area, and thus would be redundant.
(2) Edge depth file.–Alternatively, you can specify a comma-delimited ASCII file that provides unique edge depths for each edge type (i.e., each pairwise combination of patch types). Simply click on the Edge Depth File button and navigate to the appropriate file. The file must be given in the form of a square two-way matrix, where each row represents a focal class and each column represents an adjacent or abutting class, and the cell values are the edge depths in meters. The format for this file is as follows:
FTABLE, 1stClassID, 2ndClassID, etc.
1stClassID, EdgeDepth_1-1, EdgeDepth_1-2, etc.
2ndClassID, EdgeDepth_2-1, EdgeDepth_2-2, etc.
etc.
• FTABLE must be specified in the first cell.
• 1stClassID is an integer value corresponding to a class value.
• 2ndClassID is an integer value corresponding to a class value.
• EdgeDepth_i-j is an integer value giving the depth-of-edge (in meters) for the corresponding edge type (i.e., for the focal class designated by the row ClassID and the adjacent class designated by the column ClassID). Note, it is advisable to provide edge depths in increments equal to the cell size, because FRAGSTATS will always round up or down to the nearest cell when applying the edge mask (see Overview discussion for details).
The edge depth file must be a square matrix (i.e., same number of rows and columns), must have the same list and order of ClassIDs as row headers and column headers, should contain a record for each unique pairwise combination of patch types (classes) in the input landscape (any missing class must be missing in both the rows and columns and will be assigned a zero edge depth for all edges involving that class), and all arguments should be separated by a comma. For example, given four classes the following file would be suitable:
FTABLE,1,2,3,4
1,0,30,70,40
2,30,0,40,40
3,30,40,0,50
4,30,40,50,0
NOTE, this table can be created and managed using any spreadsheet program (e.g., Excel) and then simply saved as a comma delimited file (.csv).
NOTE, this matrix can be asymmetrical; that is, upper right and lower left halves do not need to mirror each other. Accordingly, it is important to realize that the rows represent the focal class and the columns represent the adjacent or abutting class. Let’s consider the edge depths for focal class 1 in the example above, given in the second row of the table. The edge depths represent the depth-of-edge effect for patches of class 1 abutting patches of the classes given by the columns. Thus, the class 1 (row)–class 3 (column) edge type has an edge effect of 70 m; that is, the edge effect penetrates 70 m into class 1. Conversely, focal class 3 (row) adjacent to class 1 (column) has an edge effect of 30 m. Thus, the edge effect penetrates less into class 3 than into class 1. This asymmetry may be important in many applications; for example, when urban edge effects penetrate deeply into forest, but forest edge effects penetrate very little, if at all, into urban areas.
NOTE, the diagonals are typically given a zero edge depth, but it is possible to specify a nonzero diagonal. However, the only situation in which a patch can abut a patch of the same class is along the landscape boundary when a landscape border is present (see discussion on Background, Boundaries, and Borders). In this case, it is possible to specify a nonzero edge depth, although in most cases it would not be logical to do so.
NOTE, if you have background in the image, you need to include the background class value specified in the Run Parameters dialog box in the list of classes specified in the edge depth file, otherwise all background edges will be given a zero edge depth.
• Isolation/Proximity Metrics.--If you select either the PROXIMITY INDEX or SIMILARITY INDEX at the patch, class, or landscape level, you must specify the search radius (i.e., the distance [in meters] from a focal patch within which neighboring patches are evaluated). By default the search radius is zero, but you must enter a non-zero distance before closing the dialog box or you will receive an error message in the log window. In addition, if you select the similarity index at any level, you must specify a comma-delimited ASCII file that provides unique similarity weights for each pairwise combination of patch types. Simply click on the Similarity Weight File button to navigate to the appropriate file. Each record in the file should contain a numeric patch type value for each of the two classes and a similarity wieght. The syntax for this file is as follows:
FTABLE, 1stClassID, 2ndClassID, etc.
1stClassID, SimilarWeight_1-1, SimilarWeight_1-2, etc.
2ndClassID, SimilarWeight_2-1, SimilarWeight_2-2, etc.
etc.
• FTABLE must be specified in the first cell.
• 1stClassID is an integer value corresponding to a class value.
• 2ndClassID is an integer value corresponding to a class value.
• SimilarWeight_i-j is a fraction that must range between 0 (no similarity) and 1 (maximum similarity) that gives the similarity weight for the corresponding classes (i.e., for the focal class designated by the row ClassID and the adjacent class designated by the column ClassID).
The similarity weight file must be a square matrix (i.e., same number of rows and columns), must have the same list and order of ClassIDs as row headers and column headers, should contain a record for each unique pairwise combination of patch types (classes) in the input landscape (any missing class must be missing in both the rows and columns and will be assigned a zero similarity weight for combinations involving that class), and all arguments should be separated by a comma. For example, given four classes the following file would be suitable:
FTABLE,1,2,3,4
1,1,0.8,0,0.4
2,0,1,0.6,0.4
3,0.1,0.2,1,0.5
4,0.3,0.4,0.5,1
NOTE, this table can be created and managed using any spreadsheet program (e.g., Excel) and then simply saved as a comma delimited file (.csv).
NOTE, this matrix can be asymmetrical; that is, upper right and lower left halves do not need to mirror each other. Accordingly, it is important to realize that the rows represent the focal class and the columns represent other class combinations. Let’s consider the similarity weights for focal class 1 in the example above, given in the second row of the table. The similarity weights represent the degree of similarity between a patch of the focal class and a patch of another class. Thus, a patch of focal class 1 (row) has maximum similarity to a patch of the same class (weight = 1) and a similarity of 0.8 to a patch of class 2, but zero similarity to a patch of class 3. Conversely, a patch of focal class 3 (row) has a similarity of 0.1 to a patch of class 1. In most cases, however, it is more logical to think of similarity in terms of symmetrical weights.
NOTE, the diagonals are typically given a weight of one, because the similarity of two patches of the same class is generally assumed to be the maximum, but it is possible to specify a different value.
NOTE, if you have background in the image, you need to include the background class value specified in the Run Parameters dialog box in the list of classes specified in the similarity weight file, otherwise all background edges will be given a zero weight.
• Contrast Metrics.--If you select any contrast metric at the patch, class, or landscape level, you must specify a comma-delimited ASCII file that provides edge contrast weights for each pairwise combination of patch types. Simply click on the Edge Weight File button to navigate to the appropriate file. Each record in the file should contain a numeric patch type value for each of the two classes and an edge contrast weight. The syntax for this file is as follows:
FTABLE, 1stClassID, 2ndClassID, etc.
1stClassID, ContrastWeight_1-1, ContrastWeight_1-2, etc.
2ndClassID, ContrastWeight_2-1, ContrastWeight_2-2, etc.
etc.
• FTABLE must be specified in the first cell.
• 1stClassID is an integer value corresponding to a class value.
• 2ndClassID is an integer value corresponding to a class value.
• ContrastWeight is a fraction that must range between 0 (no contrast) and 1 (maximum contrast) that gives the edge contrast weight for the corresponding classes (i.e., for the focal class designated by the row ClassID and the adjacent class designated by the column ClassID).
The edge contrast weight file must be a square matrix (i.e., same number of rows and columns), must have the same list and order of ClassIDs as row headers and column headers, should contain a record for each unique pairwise combination of patch types (classes) in the input landscape (any missing class must be missing in both the rows and columns and will be assigned a zero edge contrast weight for combinations involving that class), and all arguments should be separated by a comma. For example, given four classes the following file would be suitable:
FTABLE,1,2,3,4
1,0,0.8,0.6,0.4
2,0.8,0,0.7,0.3
3,0.6,0.7,0,0.5
4,0.4,0.3,0.5,0
NOTE, this table can be created and managed using any spreadsheet program (e.g., Excel) and then simply saved as a comma delimited file (.csv).
NOTE, this matrix can be asymmetrical; that is, upper right and lower left halves do not need to mirror each other, although in most cases it is more logical to think of edge contrast as being symmetrical. Accordingly, it is important to realize that the rows represent the focal class and the columns represent adjacent or abutting classes. Let’s consider the edge contrast weights for focal class 1 in the example above, given in the second row of the table. A patch of focal class 1 (row) adjacent to a patch of class 2 (column) has a contrast weight of 0.8; that is, it is 80% of the maximum contrast (1). Likewise, an edge between focal class 1 (row) and adjacent class 3 (column) has a contrast weight of 0.6 (i.e., 60% of maximum).
NOTE, the diagonals are typically given a zero edge contrast weight, but it is possible to specify a nonzero diagonal. However, the only situation in which a patch can abut a patch of the same class is along the landscape boundary when a landscape border is present (see discussion on Background, Boundaries, and Borders). In this case, it is possible to specify a nonzero edge contrast weight, although in most cases it would not be logical to do so.
NOTE, if you have background in the image, you need to include the background class value specified in the Run Parameters dialog box in the list of classes specified in the edge contrast weight file, otherwise all background edges will be given a zero weight.