Calculates the Area of Occupancy of a species based on either known records or predicted distribution.
One of three options: 1) matrix of longitude and latitude (two columns) of each occurrence record; 2) matrix of easting and northing (two columns, e.g. UTM) of each occurrence record in meters; 3) RasterLayer object of predicted distribution (0/1 values).
AOO is calculated as the area of all known or predicted cells for the species. The resolution will be either exactly (if spData is in meters) or approximately (otherwise) 2x2km as required by IUCN).
A single value in km2.