We've always had the capability to do this manually using two paper maps but it's very laborious and not very easy to compare like with like.
This new tool uses geo-referenced maps which are overlaid on top of the current street map, and you can decide which maps to compare.
For family historians, this has several great benefits; you can see, at a glance:
- how streets have developed since the previous map
- where new buildings are
- where streets have disappeared
- which streets have been renamed
Also, I think it will be helpful when looking at valuation rolls to see what a street looked like before or after.
The picture shows an area of Spring Gardens, Edinburgh. Notice how a bit of land to the right of St Ann's Bank House in the top map (1849) has become a row of buildings, Violet Bank, in the bottom map (1876).
Have a go at using the dual map tool, yourself, and let me know what you think.
If you want to change map when you're in the tool, click the [clear overlay] link to remove the map, then click the new map you want.
Of course, the great drawback for us is that it allows only the comparison of Edinburgh maps, however, as it has been done for Edinburgh, it presumably can be done for other places, too; and that's another great reason to get on with the geo-referencing of historical maps.