BGS Geology FAQ

BGS Datasets

What is a geology map?

A geology map is any map that provides details about rocks, sediments, faults and a whole range of observations to do with the composition and structure of the Earth.

BGS surveys geological features at 1:10 000 scale and we publish our findings digitally at this and smaller scales. The maps convey our best interpretation of what lies beneath our feet and the evidence behind the map can be derived from decades of research, countless boreholes and sampling programmes, and digital landscape analysis. Traditional survey techniques are still used, but BGS now also uses 3D modelling and visualisation to help update and improve the maps on a continuing basis.

Who uses a geology map?

Geology maps are made for a wide range of users. Some of our mapping and research is dedicated to simply understanding the Earth, the processes that modify our landscape and the role geology plays in our lives. Some users rely on our maps to work out things like resources (energy; water; minerals), construction conditions (excavations; foundations), soils and landscapes (peatlands; uplands), and hazards (flooding; landslides; contamination). We try to make maps at different scales and with different attributes so that as many users as possible can find the right map and information for their needs.

What is the geology under my house?

We have several ways for you to look at the geology beneath you. Our map viewers page is a good place to start, or you could go straight to our Geology of Great Britain viewer. If it’s a paper map you want to see, we recommend a visit to the BGS maps portal.

What are the different colours on the map for?

The different colours, patterns and linestyles are to show differences in rock age, rock type or some form of process or characteristic that makes the ground ‘different’ geologically from its surroundings. Many geological units have had traditional colour schemes since the earliest map made by William Smith 200 years ago. The colours and patterns allowed early mappers to show 3D geological complexity on a 2D piece of paper. The advent of digital data means that we can interrogate 2D and 3D data with a mouse click, but we retain the familiar colours and map styles so that users can see how the digital world relates to traditional geological maps.

Where can I purchase paper maps?

Paper maps are available from our online shop. You can also view our catalogue of 6000 digital scans of paper maps in our maps portal.

Where can I get digital data?

Data is typically available under licence (i.e. for a fee). However, an increasing amount is available for view or download. Our datasets page can provide details of the different datasets available. Each page will provide information about data coverage, prices, formats and who to contact. Many products also offer sample data downloads and user guides to help you decide if the data is suitable for you.

I don’t have a GIS. Can I still view the data?

Yes! Our map viewers page is a good place to start: there are links there that will take you to various apps and online services, or you could go straight to our Geology of Great Britain viewer. If you want to see more than just geology data, our GeoIndex is an online data and GIS service that covers a very wide range of geoscience research.

If it’s a paper map you want to see, we recommend a visit to the BGS maps portal.

How often do you update the geological maps?

Our mapping is updated by a combination of strategic survey and ad hoc review, normally as part of our wide research activities. These generate a range of new data and corrections across Great Britain and the BGS Geology team have a year-round programme of editing and updating. It can take a while to fully resolve a new area of mapping or reconstructed data, so our map revisions are published periodically — typically every two to three years.

Why does the geology sometimes not ‘match’ across sheet boundaries in the 1:50 000-scale digital data?

Discrepancies in mapping or descriptions of geological materials across map boundaries are predominantly due to the age of the underlying survey that created the data. Modern surveys can resolve new information from a range of sources not previously available to earlier surveys. In addition, new interpretations for geology can evolve over time, allowing more recent survey campaigns to add extra details or map refinement.

Reducing the occurrence of map-edge issues is an ongoing task, with new data and techniques being applied all the time. However, a geological map is an evolving product so there may always be some discrepancies between parts of the map derived from different survey campaigns or methods.

Why does the BGS Geology 50k data not contain fault ticks or dip/strike data?

Traditionally, ‘fault ticks’ (hanging wall identifiers) and dip/strike data have been shown on paper mapping using cartographic symbology.

Our process to capture the paper maps into a digital database were partly successful in transcribing some of the information needed to accurately portray the faults. However, our data quality checking procedures identified that subsequent conversion of these features into alternative spatial data formats could result in the data becoming corrupted. We are trialling a more robust method of handling fault hanging-wall information for future releases but in the meantime this data is withheld.

Similarly, our process to capture cartographic structural data such as dip/strike from paper maps and convert them into an intelligent digital format is ongoing. We are currently working on a new database of structural information (derived directly from our survey-scale activities) and hope to release this data soon.

Our map portal contains scans of all the last-printed 1:50 000 geological sheets, so you can utilise this archive to confirm fault throws and structural data as published on previous paper maps. However, please note that some of these maps will show geology that has now been significantly modified in the BGS Geology 50k dataset (i.e. the digital mapping is more up to date).

Why are there mapping discrepancies between the 1:10 000 and 1:50 000 layers?

It is not unusual for discrepancies to occur between the two different scales of mapping. Traditionally, the main reason for this is the generalisation and simplification of the map face content from the 1:10 000 ‘survey-scale’ original mapping. The generalisation makes the map objects clearer to read at the smaller scale (1:50 000), whilst the simplification of the terminology used to describe the lithologies and ages will ensure that the modified map objects still convey the meaning and context of the original survey observations.

BGS has not always published its 1:10 000 survey-scale original mapping, focusing on the 1:50 000 maps instead. Digitisation of the original 1:10 000 paper mapping is still ongoing and so the 1:10 000-scale digital archive is less complete in coverage compared with the 1:50 000 digital archive. Additionally, any updates to the mapping at either scale can occur at any time, and non-sequentially (i.e. a regional study of geology at 1:50 000 scale may have made changes to mapping that is not yet adopted in the 1:10 000-scale data).

It is important to note that there may also be discrepancies between the paper and digital versions of the maps and the two different scales. This is because both scales of mapping are subject to ongoing correction and generalisation over time. The digital mapping will show the latest interpretation of the geology.

Why are there differences between the hard-copy maps and the geological data shown on the online viewers? Which one should I use?

BGS no longer updates the traditional 1:50 000-scale hard-copy (paper) maps of geology. The digital mapping available online represents our latest ‘version’ of geology for Great Britain. This means that the paper maps are now superseded and the online digital map resources are the most appropriate for ground investigation etc. The last geological sheets to be provided in print format were Derby (sheet 125) and the Isle of Wight special sheet (in 2014 and 2015 respectively). All of our map updates since 2011 have been for digital platforms only.

We do still provide hard-copy output for 1:10 000-scale data (where digital may not yet be available) and we provide a print on demand service for users wanting hard-copy from 1:50 000 digital mapping. Most of the legacy paper maps are available as freely viewable scans and many of these maps can still be bought in folded or flat paper formats for users seeking the original mapping in a traditional format. Please note: all maps in this paper archive are now superseded, even the most recent ones.

We recommend that all professional users now refer solely to the data available on our GeoIndex platform as this provides the most comprehensive and up-to-date digital map data. Users are advised to only refer to traditional paper mapping (or the scanned paper map archive in the BGS map portal) for legacy purposes, or to utilise the map marginalia, or to assess how the interpretation of the geology may have changed through time.

Why are there different rock descriptions used on the digital and paper maps?

In terms of rock descriptions, all of our digital maps use two common referencing systems, or dictionaries: the BGS Lexicon of Named Rock Units for stratigraphy and theBGS Rock Classification Scheme for lithology. These dictionaries describe age and lithology for most units. This system is updated with new data in a digital format only. We no longer support legacy map codes such as f2, f5 etc., but the BGS Lexicon will identify previous names for a unit if its name has changed since 1990 or where legacy nomenclature is still being used as common parlance, e.g. ‘Keuper Marl’.

Which online viewer is best for me to use?

The Geology of Great Britain viewer is a handy tool for viewing the main geology dataset at 1:50 000 scale. It is designed for general use by the public, as is our iGeology platform for smartphones.

We recommend that all professional users now refer solely to the data available on our GeoIndex platform as this provides the most comprehensive and up-to-date digital map data, as well as a useful resource of supporting additional materials. Users are advised to only refer to paper mapping (or the scanned paper map archive in the BGS map portal) for legacy purposes, or to utilise the traditional map marginalia. The 1:50 000-scale paper maps are no longer updated by BGS. Many of the 1:10 000-scale (and earlier ‘six-inch’) paper maps are still available, but these too are gradually being replaced by all-digital content.

Why is the coverage of the 10k and 25k data not complete?

Having captured most of the 1:50 000 mapping, BGS is gradually capturing the larger-scale 1:10 000 paper map archive (BGS Geology 10k). The next release of BGS Geology 10k (Version 3) will include a total of 4970 sheets. A further 560 sheets are still in progress.

The 1:25 000 survey-scale mapping is only available in some small areas of Wales and Scotland. We expect all the available sheets at this scale to be completed and published soon as part of the BGS Geology 10k (Version 3) release.

How often do you update the geological maps?

Our mapping is updated by a combination of strategic survey and ad hoc review, usually as part of our wide research activities. These generate a range of new data and corrections across Great Britain and the BGS Geology team have an ongoing programme of editing and updating. It can take a while to fully resolve a new area of mapping or reconstructed data, so our map revisions are published periodically, typically every three to five years.

I think the geology map might be wrong. What can I do?

We make every effort to ensure that our digital data reflects our best understanding of the geology of the UK and its continental shelf, but sometimes our interpretations need to be revised as new evidence (such as boreholes) are obtained. We are currently working on a web service to improve notifications of errors that have been found and corrected; we hope to make this available soon. If you think you have spotted a problem with our datasets please let us know.

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