Standards: BRUs (Biological Recording Units)

(also known as Basic Recording Units)

World Geographical Scheme for Recording Plant Distributions

Adopted 1992 as TDWG standard #2

A four-tier hierarchial system; distributions to be coded at the lowest level possible

General principles:

Off-shore islands and island groups are separated from the mother country
The major countries (in terms of size) are split into their constituent geopolitical units
Major geopolitical boundaries are observed, so that ISO countries can almost always be built up from their constituent BRUs

Levels:

Level 1 - 9 categories

Level 2 - 152 categories

Level 3 - 364 categories

Level 4 - 574 categories

Reference (Hollis & Brummitt, 1992)