There are more than 1,200 geological formations and members (rock units) in the 1:100,000 Bedrock Geology map. Rock properties such as colour, grain size and type, origin, fossil and mineral content are used to define formations and members. A lot of these properties are not relevant for groundwater flow through the rocks (for example, type of fossil).

To produce this dataset, all of the formations and members were assessed and assigned to one of 27 'Rock Unit Groups' that are significant for the way that groundwater might flow through those rocks. The Rock Unit Groups also take into account geological age.

This map is to the scale 1:100,000. This means it should be viewed at that scale. When printed at that scale 1cm on the map relates to a distance of 1km.

It is a vector dataset. Vector data portray the world using points, lines, and polygons (areas).

The data is shown as polygons. Each polygon holds information on the rock unit group name, code and a unique id.