The elementary mapping unit
The elementary mapping unit (EMU) is formed by the intersection of the soil map, administrative units and grid. The elementary mapping unit is fundamental to the system, and any change in any of these three components has major implications. The EMU is not given a unique identifier in the database, but is stored as a (unique) combination of its properties, i.e. soil mapping unit number, grid identifier, administrative unit code and its surface area. The ELEMENTARY_MAPPING_UNIT table contains the following fields:
GRID_NO: identifier for the grid [-] NUTS_CODE: code identifying the administrative region [-] SMU_NO: code identifying the soil mapping unit [-] AREA: surface area [m2] When producing the EMU coverage, care must be taken to carefully clip the individual coverages. A straightforward intersection of the three underlying datasets could produce many artefacts, especially around country borders and shorelines, and result in EMUs that are not properly defined.