Definition

The area contained within the shortest continuous imaginary boundary which can be drawn to encompass all the known, inferred or projected sites of occurrence, excluding cases of vagrancy. ¹

Further detail:

Extent of occurrence is a parameter that measures the spatial spread of the areas currently occupied by the taxon. The intent behind this parameter is to measure the degree to which risks from threatening factors are spread spatially across the taxon’s geographical distribution. It is not intended to be an estimate of the amount of occupied or potential habitat, or a general measure of the taxon’s range ². Extent of occurrence can often be measured by a minimum convex polygon (the smallest polygon in which no internal angle exceeds 180 degrees and which contains all the sites of occurrence) ¹

International Union for Conservation of Nature (IUCN) 2012 ¹

International Union for Conservation of Nature (IUCN) 2014 ²

Note: CITES uses the same definition for the term 'species area of distribution'. The two terms can therefore be seen as equivalent.