The NLS (National Library of Scotland) maps website is a treasure trove for family historians. It holds thousands of old maps, including Ordnance Survey maps of Scotland, England and Wales from the 1840s to the 1970s, maps of Scotland dating as far back as the 17th century, estate maps, town plans and military maps.
One of the NLS maps’ website’s most useful features is the ability to overlay one map on top of another, with the top layer made semi-transparent so you can compare it with the one beneath. This allows you to compare how a place looked during your ancestor’s life with how it appears now or at some other point in history.
On the NLS maps’ website, the map overlay can be accessed via the georeferenced maps section. Once you’ve found and annotated a map, you can print or save it. You can also access the feature via other parts of the site, including ‘Find by Place’ and ‘Browse by Mapmaker’. Target the map you want, then zoom in to your chosen location and hold Alt as you click on the map to switch to a georeferenced maps view.
Open your web browser and head to the NLS maps website. Click ‘Georeferenced Maps’ to access the overlay feature directly. Click ‘X’ to close the brief tutorial after reading, or scroll to the bottom and click ‘Don’t show this message again’ to stop the tutorial appearing in future.
Click the ‘Background map’ dropdown menu at the top of the map pane to reveal a choice of 16 backgrounds spanning terrain (Bing and ESRI), maps – including two historic options (OS 1900s and 1920s), and topography (LiDAR). Select one and it’ll appear behind the historic map.
Use your mouse’s scroll wheel to zoom into the map towards the area you wish to examine. You’ll see that by default the OS one-inch map from 1885–1900 has been selected – you can change this instantly using the ‘Select a category’ and ‘Select a map/map series’ dropdown menus.
By default, only the historic map overlay is currently visible. Beneath the map overlay options you’ll find a transparency slider. As you drag this left you’ll see the terrain or background map you selected appear underneath the map. The best setting to see both maps is usually 30–45 per cent transparency.
You can now switch both the background map and the overlay without losing your position or opacity settings, allowing you to see how the area in question has changed over the years. Rotate your maps by holding the Alt + Shift keys together as you click and drag the cursor left or right.
If you’d like to zoom out for an overview of the area, but don’t want to lose your map position (such as an ancestor’s street address), then hold the Shift key and click on the map. The marker will appear on-screen to guide you back to that spot as you zoom back in later.
Click ‘Full Screen/Draw’ and the control panel on the left will vanish to leave you a full-screen view of the map and its overlay. The transparency slider remains at the top, as does the option to create or remove a marker. Click ‘Explore Georeferenced Maps’ to return to the main view.
You can also label the map using a selection of drawing tools accessible under the ‘Draw features’ dropdown menu in the top-right-hand corner: point, line string, polygon and circle. Select a tool and click on the map to lay down your first point, and click again to draw the object.
Select 3D and you can view a pseudo-3D view of your map. This works in the same way as the regular top-down view, but you’ll see that the view is skewed. Use the ‘Change vertical exaggeration’ slider to alter the angle of view – drag left to make it flatter, right to make it steeper.