The data comprises primarily polygons (or areas) and lines. Each polygon is attributed with information based on the name (often lithostratigraphical) of the unit and its lithology or composition. These polygons are arranged in up to four themes as available: bedrock geology ('solid'); superficial deposits ('drift' or Quaternary); mass movement (mostly landslide); and artificial (or man-made ground). The lines include thin beds (such as coal seams and fossil bands) faults, mineral veins and some landforms. Coverage of point data, e.g. dips and strikes, is limited and is not yet available.Back to top
The digital geological maps typically show up to four polygon themes as described below.
|Bedrock (or 'solid') geology||Mostly consolidated natural rocks||Pre-Quaternary age, older than about 1.8 million years|
|Superficial (or 'drift') deposits||Unconsolidated natural in situ superficial or surficial deposits||Quaternary age, younger than about 1.8 million years|
|Artificial ground||Man-made deposits, mineral workings, re-modelled or altered ground||Recent|
|Mass movement deposits||Primarily landslide or foundered ground, moved down slope under gravity||Quaternary age, younger than about 1.8 million years|
These datasets are labelled or attributed with a variety of codes which provide the name of each rock unit or deposit and composition as well as additional information e.g. maximum age.
For example a polygon may have a LEX-RCS geological codes which provide the name of each rock unit or deposit (via its LEX or Lexicon code) and composition (via its ROCK or lithology code); an example is MMG-MDST (Mercia Mudstone Group - Mudstone). The Lexicon Codes and related information can be accessed in the Lexicon.
A full list of definitions for each attribute code can be found in the User Guide Provided by the BGS:
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All linear features are digitised and geologically attributed like the polygons. Their availability depends if the features were recorded when the area was mapped. For the 1:50,000 data they are organised into a number of categories:
Many of the linear features are attributed generically, e.g. rock beds are identified as coal seams or marine bands, however, these rock units and fossil horizons can also be identified with LEX-RCS codes in the same way as polygons and carry the same associated information fields. Thus particular coal seams or marine bands may be identified with specific LEX codes e.g.:
YCL (Yard Coal, Leicestershire) see Lexicon
AGMB (Aegiranum Marine Band) see Lexicon
Similarly other linear features such as faults and mineral veins may also be attributed with more specific information e.g. the name of the fault or the composition of the mineral.Back to top
Do not over-enlarge the data; for example do not use 1:50 000 nominal scale data at 1:25 000 or 1:10 000 working scale. The scale of the original information is indicated by the nominal scale attribute (NOM_SCALE) embedded in the data.
The 1:50 000 scale geological maps are generalised from detailed 1:10 000 scale maps by cartographic selection, modification, simplification or exaggeration. The generalised geological lines were fitted to Ordnance Survey 1:50 000 (or 1:63 360) topographic bases available at the time of publication, as indicated by the nominal OS year attribute (NOM_OS_YR). The digital data do not necessarily fit other topographic bases, including more modern OS ones.
The 1:50 000 data may be used as a guide to the geology at a local level, but should not be relied on for site specific geology. If detailed information is required then the 1:10 000 (or 1:10 560) scale maps or digital data, usually the most detailed interpretations available, should be consulted.
Each Geology Digimap digital tile is typically based on the latest 1:50 000 (or 1:63 360) scale geological map. For some maps, especially in areas of complicated geology, the Bedrock and Superficial (formerly 'Solid' and 'Drift') geology themes are published as separate editions. Some changes may have been made to the published linework but major revisions have generally been avoided. In exceptional cases, where the published maps are seriously deficient and new mapping is available, geological lines have been imported from recent 1:10 000 or 1:25 000 scale maps. Those geological maps that were only available as paper copies have been digitised for Geology Digimap. Recently published maps, compiled digitally, have been reprocessed to the same standard. In some areas where there are no suitable geological maps published, new geological lines have been compiled for Geology Digimap by fitting the best available old linework to modern topographic bases.Back to top