Usual administrative units are too heterogenous for regional statistics. To make regions comparable, territorial units of similar population size are required. For the European Union and further states being associated in some way or another the NUTS (Nomenclature des unités territoriales statistiques) classification has been developed in 1980 and is being updated triennially.
There are four NUTS levels 0,1,2 and 3. Every region is designated a code consisting of two to five characters. The first two characters denote the state (the usual ISO-3166 two letter code – Greece being an exception as it is referred to with EL instead of GR). The characters following it in case of NUTS 1,2 and 3 form a hierachical system. So for example DE21H (Munich) belongs to DE21 (Oberbayern) belongs DE2 (Bayern / Bavaria) belongs to DE (Germany).