EOO and AOO as used by the IUCN Red List are two different ways of looking at the geographic range of a species. Estimates can be made in a variety of ways, see the CATS tool developed at Royal Botanic Gardens, Kew. Another way is to make use of the high resolution images on Google Earth where it is possible to 'draw' your species range based on your knowledge of an area or the habitat in which it occurs. One way to do this is as follows:
Aside from Google Earth, obviously, you will also need to download GE Path here.
1. In Gogle Earth browse to the location of your species.
2. Click the 'Add Polygon' button and add a name
3. Click on the map to start drawing the polygon and keep clicking along the boundary of your forest or patch of vegetation.
4. Setting the Opacity of the polygon in the Style.Color menu to 50% alows you to see the image and the polygon shape at the same time.
5. In the 'Places' menu to the left of the map you should see your polygon listed. Right click on it and copy. This will copy the data associated with the polygon.
6. Open notepad or another text editor and paste the data into the text window. Save the file as 'yourpolygon.kml'
7. Open GE Path and Open the 'yourpolygon.kml' file you just created
8. Set the Method for area calculation - two settings depending on whether you have a large or small polygon.
9. Click Run and the results will be displayed in the Area/Perimeter section at the bottom of the GE Path window.
The area measures can the be compared with the IUCN Red List Criteria thresholds to determine whether species is threatened or not.