GeoCAT glossary

Browse our GeoCAT glossary terms.

GeoCAT tool

AOO (Area of Occupancy)

The red cells show ‘occupied’ cells and represent AOO. Area is given in km2. The AOO calculation can be summarised in the following formula:

AOO = number of occupied cells * area of individual cell

EOO (Extent of Occurrence)

The convex hull or minimum convex polygon, used to define EOO, is a line drawn around all distribution points with no internal angle exceeding 180º. This is the same as imagining an elastic band being pulled over all the points. The value reported for EOO is the area within the black line and is measured in km2.The convex hull can only be drawn when there are at least three unique distribution points or localities.

Geographic range

The geographic range or distribution of a taxon is the area in which it can be found. For Red Listing it is usually the native or natural range of a species and may include inferred or projected sites of occurrence. 


To give an "object" a spatial reference. For most cases that is giving a latitude or longitude to a species collection, sighting or literature reference.

Decimal latitude and longitude

The degrees, minutes and seconds of a locality expressed in decemial degrees. Where:
Degrees + minutes/60 + seconds/360 , where W or S are negative. Example (51 29' 07" N, 0 17' 30" W or 51.48528 -0.291667)

IUCN Red List

For more detail see the IUCN Red List


Occurrences can include observations, herbarium/museum collections, images, DNA sample and any other record of the existence of a biological entity.

Red List Categories and Criteria

See Wikipedia and IUCN Categories and Criteria


Comma separated values, simple and common format that the majority of spreadsheet and databasing programs can read.


Keyhole markup language, XML schema for geographic data. Predominately used in Google Earth.

.GeoCAT & .RLA

The file used to store information relating to a GeoCAT project. This file is created when a project is saved and can be uploaded to.