National overview maps
Two national overview maps are available. One shows the extent or area over England and Wales where rock units that are designated as principal aquifers by the Environment Agency are present at the surface and below ground. The second map shows the extent of the six major (potentially gas-bearing) shale units present at the surface and below ground.
OD refers to u003ca href=u0022http://en.wikipedia.org/wiki/Ordnance_datumu0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003eOrdnance Datumu003c/au003e. It is the common reference level against which all vertical elevations (heights) on maps are related to. As a simplification it can be considered as equivalent to sea level. On the maps published by BGS, where a height is given as a positive number then this is above OD and where negative below OD.
Contact
Please contact BGS Enquiries for more information.