I just did the coolest thing!
The Welsh National Archives are asking for our help to index and orient the tithe maps of Wales from the 1840s! I was able to locate several data points that matched a modern Ordnance Survey map with the 1843 Tithe map for Llanfoist, Monmouthshire! (By the way, I also learned that Welsh spelling for Llanfoist is Llanffwyst. It makes a difference.) You can see my work here. Click on "visualize" and you will see the overlay based on my data points.