Core area index (Core area metric)

## Usage

lsm_p_cai(landscape, directions = 8, consider_boundary = FALSE, edge_depth = 1)

## Arguments

landscape

Raster* Layer, Stack, Brick, SpatRaster (terra), stars, or a list of rasterLayers.

directions

The number of directions in which patches should be connected: 4 (rook's case) or 8 (queen's case).

consider_boundary

Logical if cells that only neighbour the landscape boundary should be considered as core

edge_depth

Distance (in cells) a cell has the be away from the patch edge to be considered as core cell

tibble

## Details

$$CAI = (\frac{a_{ij}^{core}} {a_{ij}}) * 100$$ where $$a_{ij}^{core}$$ is the core area in square meters and $$a_{ij}$$ is the area in square meters.

CAI is a 'Core area metric'. It equals the percentage of a patch that is core area. A cell is defined as core area if the cell has no neighbour with a different value than itself (rook's case). It describes patch area and shape simultaneously (more core area when the patch is large and the shape is rather compact, i.e. a square). Because the index is relative, it is comparable among patches with different area.

Percent

0 <= CAI <= 100

### Behaviour

CAI = 0 when the patch has no core area and approaches CAI = 100 with increasing percentage of core area within a patch.

McGarigal, K., SA Cushman, and E Ene. 2012. FRAGSTATS v4: Spatial Pattern Analysis Program for Categorical and Continuous Maps. Computer software program produced by the authors at the University of Massachusetts, Amherst. Available at the following web site: http://www.umass.edu/landeco/research/fragstats/fragstats.html