Gazetteer Data

Wilkinson’s Gazetteer and Bibliography of the Mines and Quarries of North Wales


This page describes the background to the data that forms the basis of Jeremy Wilkinson’s Gazetteer and Bibliography of the Mines and Quarries of North Wales. In particular it addresses:

This page does not cover technical aspects of the system. These can be found on the gazetteer READ ME page.

Wilkinson’s Data

As stated on the Gazetteer front page, the Gazetteer and Bibliography data were originally compiled over a considerable number of years by Jeremy Wilkinson from Public Record Office and other sources of public record. In addition to the formal documentary sources, Wilkinson searched the second edition of the Ordnance Survey 6" maps (based on surveys from 1899 onwards) and some other maps for unnamed features such as mines, shafts, levels, quarries etc.

Wilkinson created a single record for each site (mine, quarry or other physical feature) he found. Sites with more than one name or where the named changed with time were recorded as a separate site for each name (with, where known, the same grid reference). Sites without documented names such as the mines, shafts, levels, quarries etc. mentioned above were assigned names based on named map features in their vicinity. However, where sites were more or less equidistant from several named features, the choice of name appeared arbitrary.

In addition to the site records, Wilkinson created reference records for each site. These included references to Home Office Lists of Mines, HM Mine Inspectors’ reports etc. plus some references to secondary sources such as David Bick’s The Old Copper Mines of Snowdonia. For the unnamed sites mentioned above, Wilkinson provided the 6" map county name and sheet number (though in some cases the site was not shown on the map specified but on the corresponding 25" map instead). The references also included some cross-references to other sites.

Other data included a list of company names and an association of such names to roles at sites or in organisations. Because Wilkinson used fixed-length records, some company names were truncated.

Various translations of product codes, county and parish identifiers etc. which were used to reduce space in the site and other files were incorporated in the display programs.

Wilkinson's main interest appears to have been the metalliferous mines and slate quarries of north-west Wales. Consequently, his coverage of north-east Wales, particularly with regard to coal mining is less comprehensive than for other areas.

Changes and Additions to the Data

File Structure

Wilkinson's fixed length files have been converted to variable length records and record structures have been altered as a consequence. Translations have been extracted from Wilkinson's BASIC program files and used to create separate translation files. However, the general organisation of the main data files and the relationships between them is substantially unchanged from Wilkinson's system as it stood in 2002.

Site Names

There is considerable variation between sources as to site names. To handle this:

Wilkinson's data included a approximately 1600 sites with no documentary evidence for their names. These were mostly small quarries and gravel pits (typically used for building or road materials), isolated shafts etc. Wilkinson assigned names to these sites based on nearby features (typically topographic or farm names). It was decided to revert them to just that shown on the map. The facility to search by distance from a specified grid reference, latitude/longitude or post code allows such unnamed sites near a given location to be displayed.

National Grid References

Wilkinson provided 6-figure British National grid references for sites with known locations. As far as can be ascertained, he plotted the locations from projections of microfilmed 6" map sheets. Consequently, a number of such locations were found to be in error – though generally not to a significant degree.

Grid references for additional sites and corrections to grid references in existing data where encountered have been corrected by reference to National Library of Scotland georeferenced versions of the 2nd edition OS 6" maps (or, in some cases 25" maps). Such corrections been made in accordance with The National Grid Map Reference System, Ordnance Survey 2004 i.e. the grid reference specifies the south-west corner of the 1 km (4-figure references), 100 m (6-figure references) or 10 m (8-figure references) grid square in which the feature is shown on the map.

Extensive sites such as the Penrhyn and Dinorwic slate quarries have 4-figure (i.e. 1 km precision) grid references. New records of small sites such as individual shafts have been given 8-figure (i.e. 10 m precision) grid references.

Calculations of distances between grid references and conversions from grid references to latitude-longitude coordinates (as used for indicating locations on online maps) are made from the centre of the grid square (1 km, 100 m or 10 m) as indicated by the number of digits in the grid reference.

Other Changes

Duplicated data have been eliminated and minor corrections have been made.

Truncated company names have been corrected or else marked as ‘[possible name completion?]’

Additional Data

Employment and production data

The facility to include employment (men employed above and below ground by year) and production (product output by year) data for sites has been added to the system. However, such data has been entered for only a few sites.

Secondary sources

References to a number of secondary sources have been added, in some cases with the creation of additional site records. This has been done so as to improve the coverage of the gazetteer and because in many cases such sources are more accessible than the primary sources.


To ensure comprehensive coverage, data has been included from The University of Portsmouth GB1900 Gazetteer project. This is a crowd-sourced catalogue of all named features on the 2nd edition OS 6" maps. The data was processed to extract all mining and quarrying related features (levels, mines, quarries, pits, etc.) together with their county, administrative district and grid reference. Feature names were converted to the form used elsewhere in the gazetteer so that, for instance, ‘Old Gravel Pit’ would be converted to ‘PIT’ with the product code for gravel.

A problem with the GB1900 data is that the grid references in most cases appear to be that of the text associated with a map feature rather than the feature itself. (This is understandable as it presumably avoided the need for subjective interpretation of the map by the data compilers.) However, because the existing gazetteer data records the grid reference of the sites themselves, it has caused problems with merging the GB1900 data with the existing gazetteer data in that it is not easy to distinguish between what are multiple records for the same site (i.e. alternative names), specific features of the same site which are recorded separately (e.g. Level, Shaft etc.) and what are separate but nearby sites. This is a particular problem in the Halkyn area. A utility has been written to identify clusters of sites for examination, but the output from this requires human examination of the map for each cluster and elimination of redundant records. (This task is progressing but as of June 2020 a considerable amount of work remains to be done.) Where is is not possible to associate map features such as shafts with specific mines, the individual records for such features has been retained.

Non-extractive sites

The following non-extractive sites are considered to be of relevance to the gazetteer and have been added to the data:

Additional Features


Sites with identical grid references are automatically cross-referenced. When the cross referenced site has references additional to those already shown in the current gazetteer entry, the cross reference is presented as a link to that site (otherwise the site name is just presented as plain text).

Names of sites, individuals, companies etc. are shown as links to the specific information for the site or individual etc. concerned. Thus it is possible to search for a specific mine and then follow the link for, for instance, an agent at that mine to see what other mines (with links to them) he was associated with and what his roles were at them.

In addition to the automatic presentation of cross references described above, the system has facility for the manual inclusion of plain text notes, and additional cross references such as indication of underground connections between underground slate quarries.

Map-related facilities

Ordnance Survey grid references are presented as links to their location on the UK Streetmap website 1:25,000 OS map.

Gazetteer entries for sites with known locations include links to the location on NLS 2nd edition (c. 1900) georeferenced maps, Zoom Earth and Google maps.

Gazetteer references to specific OS 6" and 25" map sheets are shown as links to the appropriate NLS sheet image.

The site search ‘display as map’ option allows the display of the location of all sites found on a map. This allows the distribution of sites matching the search criteria to be seen. Named sites are shown with a larger marker than that used for the unnamed sites. Non-extractive sites are shown on the map display with blue markers rather than the red markers used for extractive sites.


As of July 2020 the gazetteer has:

Supporting the above are:

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