Explore Georeferenced Maps - Help

This application allows a set of historical map overlays to be viewed. These are sets of maps that have had their sheet margins cropped and geographical coordinates assigned to the map images to create a seamless georeferenced layer or mosaic, positioned in its correct location in the real world. The application complements our Map Finder application that allows individual maps to be selected and viewed.

Watch a Help video on the Explore Georeferenced Maps viewer. What is georeferencing?

Explore Georeferenced Maps - main Overlay viewer

Related georeferenced map viewers

Main search process

Explore Georeferenced Maps - initial help information

1. Zoom in on your area of interest.

2. Choose the historic map overlay that you would like to search from the left-hand list, and then use the gazetteer or map to zoom in to view the detail of the overlay. Select the Zoom to this map / map series link to zoom to the selected overlay. This is particularly useful for the large-scale town plans, that only display at more detailed zoom levels. As you zoom or pan the main map, the historic overlay lists in the left-hand panel update to show just those that cover the current map view.

3. To take away the historic map overlay to display the background map/satellite layer, slide the transparency slider bar in the left-hand panel to the left.

Explore Georeferenced Maps - more detailed help information

4. View the mapping in an alternative viewer: for example, the Full Screen/Draw, 3D, or Spy Viewer.

5. You can select different background layers using the drop-down list to the upper left of the map.

6. Measure distances and areas.

7. Search using gazetteers or by National Grid Reference.

What is georeferencing?

Georeferencing assigns geographical coordinates to images of maps, so that they can be located in the real world, and then presented as an overlay on top of a satellite image layer.

Illustration of georeferencing workflow

Our typical georeferencing workflow for maps in a set or series involves:

  1. locating the four corners of the map, and cropping away the margin of the map outside of these four corners.
  2. linking these four corner points to the known real-world coordinates (ie. latitude/longitude points) of the map's corners.
  3. repeating this process for all the maps in a series, and then processing these together so that they can be displayed as a seamless layer.

For more detail on our georeferencing process, read a paper (PDF, 1 Mb) by C.Fleet, 'Creating, Managing, and Maximising the Potential of Large Online Georeferenced Map Layers', e-Perimetron, 14(3), 2019 [140-149].

Go to Explore Georeferenced Maps viewer.

Background map/satellite layers

By default, the map shows modern Bing satellite imagery as a base layer, and the OS one-inch to the mile, 1885-1900 historic map overlay on top. Select one of the historic map overlay mosaics from the left-hand list to view a different historic map mosaic. Ordnance Survey Opendata, Bing Road and Hybrid base layers, ESRI ArcGIS satellite or topo layers, 1920s mapping from the NLS Historic Maps API, or OpenStreetMap mapping are also available as base map layers from the drop-down list to the centre-top of the map. Google map and satellite layers are no longer available as the OpenLayers software we use does not support them, and also because the Google terms and conditions discourage the overlaying of other maps on top of Google layers.

Double-click on the map, or SHIFT and drag with the mouse to zoom in on a rectangle, or click the zoom slider (upper left) to zoom in on the map. Hold the ALT and SHIFT keys down and drag with the mouse to rotate the view.

Search using a Gazetteer, National Grid Reference, or Counties/Parishes

The Gazetteer at the top of the map search panel allows you to locate your area on the map using modern place names from Nominatim, using OpenStreetMap names, as well as the Definitive Gazetteer for Scotland (PDF, 135KB), developed by Bruce M. Gittings, University of Edinburgh, with funding from the Scottish Government. The OSM Nominatim gazetteer is stronger for larger settlements and street names, as well as for its global coverage, whilst the Definitive Gazetteer for Scotland is particularly strong for smaller rural features in Scotland, such as farms and hamlets, mountains, hills, rivers, streams, and lochs. The two gazetteers are searched collectively using the OSMNames technology.

The Search on OS six-inch 1888-1913 names gazetteer allows the text strings and place names from the Ordnance Survey six-inch to the mile, 1888-1913 layer to be searched. These are the initial names that have been collected from the GB1900 transcription project. This crowdsourcing project ran from September 2016 to January 2018, and collected 2.6 million names - virtually all the names on this map series covering England, Scotland and Wales. Cleaning and editing of the place name data took place during 2018 and it can be downloaded from the Vision of Britain website. The initial set of names being searched on here are the 2.52 million names where two independent transcribers both agreed on the form of the name, and so they are considered to be more accurate. Parish and county names have been assigned to the transcribed name, based on the point location of the pin, in order to reduce ambiguity and provide geographical context. It is hoped that a more complete and edited version of this gazetteer will be released in future. For further information on the GB1900 Project, see H. Southall, P. Aucott, C. Fleet, T. Pert, and M. Stoner, 'GB1900: Engaging the Public in Very Large Scale Gazetteer Construction from the Ordnance Survey 'County Series' 1:10,560 Mapping of Great Britain.', Journal of Map & Geography Libraries, 13 (1), (2017), pp 7–28, and P. Aucott, C.Fleet and H. Southall, 'The GB1900 project – from the horse’s mouth', Sheetlines 111 (April 2018).

It is also possible to search by British National Grid Reference - 2, 4, 6, 8, or 10 figures (ie. 'SE12', 'NT1234', 'TQ123456', 'SD12345678', 'SD1234567890'). You can also search using numeric Grid References as Eastings and Northings (ie. '123456,123456'). Further down, drop-down boxes allow counties and parishes (based on their names and boundaries in the 1940s) to be searched. In all cases, the map will then position to the place, National Grid Reference, county or parish that has been selected. We gratefully acknowledge OpenStreetMap, and Bruce M. Gittings, University of Edinburgh for allowing us to use these gazetteers, and the Vision of Britain project for allowing us to use these county and parish boundaries.

Go to Explore Georeferenced Maps viewer.

Zoom to this map / map series

In order to make the location and context of the historic layers clearer, the historic map mosaics are displayed overlaid on a modern Bing satellite backdrop. If your selected layer is not visible, you may need to select the Zoom to this map / map series option.

Filter maps by zoom level

Filter maps by zoom level graphic

This tick box (shown right) allows you to filter which map layers appear in the drop-down list based on your current zoom level. The tick box reads Only show maps with more detail than the current zoom level. This option works dynamically as you zoom in or out, and your current zoom level is given in brackets. The number of more detailed layers that cover the area you are looking at is given in the line below. This is especially useful in areas where we have a large number of georeferenced maps, if you just want to view those that are more detailed than the zoom level you are currently viewing.

Measurement tools

These tools, to the upper right, allow you to trace a route to measure distances or areas. Once selected, click the points on your route or area, and double-click with the mouse to stop the current measurement. Select the 'Return to normal mouse navigation' to cancel these measurement tools and use the mouse for normal selection, pan and zoom functions.

Measure distances and areas graphic

Show my location? / Geolocation

You can tick the Show my location? option in the upper left-hand panel, and (if you choose to share this data with the application) the approximate location of your device, with a radius around it, will appear as a blue dot with a circle around it on the map. This uses the W3C Geolocation API specification which provides scripted access to geographical location information associated with the user’s device, by asking the user for permission to share their location, enabling the association of the user’s IP address with the detected location.

In the lower-right of the map, the location of your mouse position is shown as a British National Grid Reference, as British National Grid Eastings and Northings, and as longitude and latitude, both in decimal and degrees, minutes and seconds forms.

To bring up the real-world location of your cursor as a pop-up so the details can be selected:

  1. hold the ALT key down and left-click with the mouse.
  2. click / tap on the Show Coordinates tab in the footer to the lower left.

When you then click or tap on the map, this will bring up the British National Grid Reference, British National Grid Eastings and Northings, and longitude and latitude of the point you have clicked on.

Capture map coordinates graphic

Go to Explore Georeferenced Maps viewer.

Adding a Marker

To add a marker to a specific place on the map:

  1. hold the SHIFT key down and left-click on the map. If you SHIFT + click a second time, it moves the marker to the second place you click.
  2. click / tap on the Add Marker tab in the footer to the lower left. Once this is selected, if you click / tap a second time, it moves the marker to the second place you have clicked / tapped on

You can remove the marker by clicking / tapping on the 'Remove Marker' link that appears to the top of the screen when there is a marker on screen. Whenever there is a marker on the map, the URL has an additional marker=[lat,lon] suffix. You can save this whole URL or pass it on to others, and it will keep the specific marker location on screen (along with other map details, etc.) when you send the URL. The Marker can be added to the main Explore Georeferenced Maps viewer and the Full Screen / Draw viewer.

Full-screen viewer graphic


Hold the [Alt] and [Shift] keys down, and drag with your cursor, or pinch with two fingers on a touch screen to rotate the map. Click/tap on the blue arrow to the upper right, or refresh the page to return to the default rotation.

Illustration of rotation graphic

Go to Explore Georeferenced Maps viewer.

Parish and County information

New parish/county information in the Explore Georeferenced Maps viewer graphic

When viewing maps in England, Scotland, or Wales at zoom levels 13 or higher, the civil parish and county that your cursor is hovering over appear as a text string to the upper right. This is based on parish and county boundaries in the 1950s. For parishes in Scotland, there is also a link to view the specific parish in the centre of the screen, highlighted in our Boundaries Viewer. We have added this to help identify the particular pre-1970s parish when viewing georeferenced maps. For viewing these administrative and other boundaries and information in more detail, please consult our Boundaries Viewer.

View this map - Specific Map Sheet Reference

For our largest georeferenced layers, the specific map sheet or sheets that your cursor is over appears to the lower right at higher zoom levels, followed by a View this map link. If you click this link, it will open the specific map sheet listed as a zoomable image in a new window. You may need to zoom right in on a specific sheet so that when your cursor moves to the lower right to click the link, it is over the same sheet.

View this map graphic

If you wish to order maps you are viewing in the Explore Georeferenced Maps viewer, you will need to view the map in our standard non-georeferenced image viewer to order it. Follow the View this map procedure above for this, or switch to the Map Finder viewer by selecting this link in the header to locate the specific map.

Go to Explore Georeferenced Maps viewer.

Linking to the viewer

The URL in your web browser address bar changes dynamically as you zoom and pan the map, and when you alter visible map layers and overlays. You may copy or bookmark the URL in your web browser address bar to save the current viewer location and zoom level.

Related georeferenced map viewers

Viewer technology

This application uses OpenLayers and MapTiler and was originally customised for the National Library of Scotland by Klokan Technologies.

We have released the OpenLayers code behind this viewer on Github for onward use. We hope that other libraries, archives and institutions may benefit from the code in making available their geographical collections.

Please email maps@nls.uk for further assistance, or to provide general comments/feedback.