These maps provide an overview, at the national scale, of the spatial relationships between principal aquifers and some of the major shale and clay units in England and Wales. The data comprises a series of occurrence maps shows the distribution of rock units that form the principal aquifers and some major shale and clay units in England and Wales. In addition, a series of separation maps show the vertical separation between pairs of shales or clays and overlying aquifers. If shale gas resources are to be developed in the UK, the implications for groundwater will need to be considered as part of any risk assessment. A step in such an assessment will be to understand and quantify the spatial relationships between the potential shale gas source rocks (including both shales and some clay units) and overlying aquifers. The datasets used to produce the aquifer maps, the shale and clay occurrence maps and the separation maps are available to download for your own use. As with other BGS data sets available for download, this will enable you to work offline to develop your own systems and methodologies using BGS data. The data used to produce the aquifer, shale and clay maps are available below as ESRI GIS and KML files.