Contagion (Aggregation metric)
lsm_l_contag(landscape, verbose = TRUE)tibble
A categorical raster object: SpatRaster; Raster* Layer, Stack, Brick; stars or a list of SpatRasters.
Print warning message if not sufficient patches are present
$$CONTAG = 1 + \frac{\sum \limits_{q = 1}^{n_{a}} p_{q} ln(p_{q})}{2ln(t)}$$
where \(p_{q}\) the adjacency table for all classes divided by the sum of that table and \(t\) the number of classes in the landscape.
CONTAG is an 'Aggregation metric'. It is based on cell adjacencies and describes the probability of two random cells belonging to the same class. \(p_{q}\) is the cell adjacency table, where the order is preserved and pairs of adjacent cells are counted twice. Contagion is affected by both the dispersion and interspersion of classes. E.g., low class dispersion (= high proportion of like adjacencies) and low interspersion (= uneven distribution of pairwise adjacencies) lead to a high contagion value.
The number of classes to calculate CONTAG must be >= than 2.
Percent
0 < Contag <=100
Approaches CONTAG = 0 if all cells are unevenly distributed and 100 indicates that all cells are equally adjacent to all other classes.
McGarigal K., SA Cushman, and E Ene. 2023. FRAGSTATS v4: Spatial Pattern Analysis Program for Categorical Maps. Computer software program produced by the authors; available at the following web site: https://www.fragstats.org
Riitters, K.H., O'Neill, R.V., Wickham, J.D. & Jones, K.B. (1996). A note on contagion indices for landscape analysis. Landscape ecology, 11, 197-202.
landscape <- terra::rast(landscapemetrics::landscape)
lsm_l_contag(landscape)
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