Land components are grouped into larger entities called land systems, which were the mapping units used for the salinity audit in Tasmania (2000). Land systems are areas of land with the same annual rainfall, geology, altitude, topography, soils and vegetation. Over 400 land systems have been recorded in Tasmania and have been published by the department as seven Regional Reports. Each land system is described by a six-digit code, based on rainfall, geology, surface rock or sediment, altitude, landform, and a final unique land system number e.g. 173121.