Despite the title's suggestion that this is a geological map, it is much more. It not only shows the standard cartographical features, such as roads, railroads and stations, canals, steamboat passages, towns, cities, counties, and distances for all of the British Isles, it is also an electoral map, as it indicates the number of parliamentary seats for each borough.
Electoral representation was a topic of particular importance in early- and mid-19th century Britain. Population decline in many formerly important centers combined with the implementation of representation policies that were hundreds of years old meant that many towns and villages with only a few dozen residents or even less, had the right to elect members of the House of Commons. Newer industrial centers such as Manchester, meanwhile had no representation at all. The electoral reforms of 1832 revised this system to provide at least nominally equitable representation.
By including this electoral data, the map maker, James Wyld, the younger (1812-1887), added a human element to the otherwise purely structural elements of the maps it is a map of Brits as well as of Britain.