A collection of hydrogeological maps created by the British Geological Survey between 1967 and 1994. The maps in the collection cover aspects of groundwater availability, exploitation and quality, and were published at various scales from 1:25 000 to 1:625 000. A hydrogeological map is a specialized type of map that illustrates the distribution and characteristics of hydrogeological features in a particular area. Hydrogeological maps of the UK provide information on major aquifers, including geological and lithological information, surface drainage systems and water quality issues. The 23 maps show information on surface water features, the three dimensional geometry of aquifers, groundwater levels, abstractions and quality including saline intrusion in varying amounts of detail. They range in scale from 1:625 000, for the national map of the hydrogeology of England and Wales, down to 1:25 000 for some of the smaller regional maps. These maps are important tools for understanding and managing groundwater resources, as well as for addressing water-related environmental issues. These maps are hard-copy paper records stored in the National Geoscience Data Centre (NGDC), and are delivered as digital scans through the BGS website.