Ordnance Survey Maps - Six-inch England and Wales, 1842-1952

Cross-posted, with a bit of editing, from the Devon History Society: this extremely good resource is worth checking out if you're interested in historical / geographical research for the UK: the Ordnance Survey Maps - Six-inch England and Wales, 1842-1952 website run by the National Library of Scotland.
I don't normally post purely information-y stuff, but this is deeply deeply cool.

Ordnance Survey Maps - Six-inch England and Wales, 1842-1952 offers three basic views:

• Individual sheets using a zoomable map of England and Wales.
• A seamless zoomable overlay layer (1888-1913) on modern Google and OS maps (you use a slider control to fade between the map and modern views).
• A seamless zoomable layer (1888-1913) side-by-side with modern Google and OS maps (a moveable cursor cross simultaneously appears on both views).

The comparison maps are georeferenced - that is, adjusted to the same coordinate system - so that you can make very precise identifications of old features in relation to new.

National Library of Scotland Map Images
Low-resolution screenshot for non-commercial illustration purposes

All of these views provide a text search by county or place; measurement tools for distance and area; a choice of background map (Google, Bing, OS, Open Street Map), pop-up map key, and print facility. The site also offers other maps - for instance, one-inch OS maps for several decades - viewable standalone without the overlay, and these can be ordered at reasonable prices as photocopies up to A0 and electronic formats.

The non-commercial Terms of Use are extremely reasonable - "You are welcome to use images, printouts or photocopies of maps for non-commercial, educational and private purposes. This includes use in a free exhibition or lecture, or in a university thesis" - requiring only attribution. Low-resolution web publication, of limited size and map extent, is similarly allowed.

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Just a few examples of what you can do with it: look at this comparison of Ladram Bay, showing the location of the now-collapsed Ladram Arch; or this one showing old footpaths below Coxe's Cliff near Branscombe (I'm going to check this out); or this one showing the now-overgrown Valley of Rocks at Watcombe; or this one showing the now-defunct hamlet of Blackgang, either destroyed by coastal erosion or incorporated into the Blackgang Chine theme park; or this one showing the Alverstoke House of Industry; or this one showing how old railway lines are still preserved in Gosport footpaths and housing developments.

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Note:
I've previously used the semi-commercial Old Maps ("Britain's most comprehensive historical map archive comprising site centred historical maps covering England, Wales and Scotland"), but lately I've become very disappointed with their increasingly anal restrictions on non-commercial use.

You used to be able to view and use (with reasonable conditions on attribution) clips of high-resolution historical Ordnance Survey maps, right down to majorly deep zoom levels, for all their maps of eras dating from the 1860s. As with any such setup, this free use would be subsidised by commercial use. But now they've semi-crippled the non-commercial view. On most of the maps, a screen blank with the message "Subscribe to view mapping at this zoom level" kicks in so soon that you often can't even zoom deeply enough to read smaller location names on the map. The strategy is understandable but shortsighted; people are going to go elsewhere, and I certainly have.

Also check out Oldmapsonline.org - this is a majorly good source ("created by a collaboration between The Great Britain Historical GIS Project based at The University of Portsmouth, UK and Klokan Technologies GmbH, Switzerland") that aggregates a very large collection of historical maps from various online sources such as the Ordnance Survey, A Vision of Britain, the David Rumsey Map Collection, and so on.

- Ray