The linking of weather stations to specified postcodes is based on expert advice from the Met Office. Linkages are reviewed annually to ensure that stations are as representative as possible of the conditions in the areas they cover. In making its recommendations the Met Office examines the Geographic Information System database showing topography, postcode areas, weather stations, built-up areas and 1 km-gridded winter mean air temperature for 1981 to 2010, i.e. the latest 30 year measurement of winter mean temperature used to calculate various weather parameters. It is not feasible for the cold weather payment scheme to reflect precisely all local temperature variations, and the variable terrain in the UK makes weather station selection complex. The aim therefore is to achieve sensible national coverage with a reasonable level of local sensitivity.