Calculates various statistics to measures the connectivity of a set of polygons.  To connect the polygons, a line is drawn from the centroid of one polygon to the next until all of the polygons are connected.  The results are stored in global variables.



CONNECTIVITY <in_cover> {out_cover} [selection_file} {dispersal_distance} {total_passes}




<in_cover> - the input polygon coverage.


{out_cover} - the name for the output line coverage.


If not specified, the line coverage is not saved.


{selection_file} - the name of a selection file that identifies which polygons to analyse.


If not specified, all polygons are used.


{dispersal_distance} - used in calculation of .cnt$index3.


If not specified, 0 is used.


{total_passes} - total number of passes made through the network of polygons.


No two polygons can be connected to each other more than once.


If not specified, 1 pass is made.





The results are stored in four global variables:


.cnt$index1 - the mean connection length between polygons relative to a theoretical maximum.  The value ranges from 0 (very low connectivity) to 100 (very high connectivity).


.cnt$index2 - Same as index1, but uses root mean squared.


.cnt$index3 - the percentage of connections less than or equal to the {dispersal_value}.


.cnt$index4 - the percentage of the length of the connection line that falls within polygons.





- This AML assumes the polygons are roughly the same size.