The UTM series of maps are based on 1:250 000 base maps published by the Ordnance Survey. Mapping is divided into squares which cover 1 degree by 1 degree of latitude / longitude in the Universal Transverse Mercator (UTM) projection, and coverage extends offshore and onto the continental shelf. The UTM series are available in three different themes: - Solid geology (complete coverage within the mapped area, including most of the UK continental shelf) - Sea bed sediments (coverage for most offshore areas) - Quaternary geology (coverage for the UK sector of the North Sea, Irish Sea and the Atlantic margin) Also included within this series are two small-scale (1:500 000) bedrock geology maps of the Central Rockall Basin and North Rockall Basin. These maps supersede the older quarter-inch series of maps which were published for England / Wales and Scotland. Geological maps represent a geologist's compiled interpretation of the geology of an area. A geologist will consider the data available at the time, including measurements and observations collected during field campaigns, as well as their knowledge of geological processes and the geological context to create a model of the geology of an area. This model is then fitted to a topographic basemap and drawn up at the appropriate scale, with generalization if necessary, to create a geological map, which is a representation of the geological model. Explanatory notes and vertical and horizontal cross sections may be published with the map. These maps are, for the most part, hard-copy paper records stored in the National Geoscience Data Centre (NGDC) and are delivered as digital scans through the BGS website.