(C123) Traversability Index

t_ir =     least cost hull area around the r^th cell in the focal patch type (i).

z_i =      total number of cells in the focal patch type (i).

t_max = maximum least cost hull area around a cell of the focal patch type (i) given minimum resistance.

Description

TRAVERSE equals the sum of the least cost hull area across all cells in the focal patch type, divided by the number of cells in the focal patch type (i.e., the mean least cost hull area for the focal patch type), divided by the maximum least cost hull area; multiplied by 100 to convert to a percentage.

Units 

Percent

Range

0 ≤ TRAVERSE ≤ 100

TRAVERSE equals 0 when the focal patch is a single cell and it is surrounded by hostile patch types that prevent any movement (i.e., function as barriers). This is achieved when the resistance coefficient for the neighboring patch type(s) is greater than the user-specified bank account for the focal cell. TRAVERSE equals 100 when the focal patch is surrounded by minimally resistant patch types (i.e., resistance weight = 1).

Comments

Traversability index is computed at the cell level and then averaged across cells in the focal patch. As a result, this metric requires substantial computations and may take considerable time to compute for a large landscape. In addition, this metric requires the user to specify an appropriate resistance matrix containing coefficients for each pairwise combination of patch types, as well as a scaling factor that governs the size of the maximum least cost hull; that is, the size of the area surrounding the focal cell that is accessible given minimum resistance. The size of maximum least cost hull is based on a user-specified maximum distance or neighborhood distance. Based on this distance, FRAGSTATS computes the “bank account” needed to achieve a circular least cost hull with a radius equal to this distance.