There don't seem to be aerial photos of the areas I'm mapping, which is a shame as I'd really like some confirmation :) So, for example, I went out and specifically walked Victoria Road in Saltaire (which is actually one of the wider ones) - keeping to one side of the road, and generally trying to maintain a 'straight' trace (here @Chris%20Elston/traces/229059) . I also made a point of sighting down the length of the road, and it's damn near straight (Saltaire was built in the late 1800s by the local mill owner Titus Salt as a model village - I'm pretty sure he'd have specified a straight road ;) ) Yet the trace shows quite a big deviation. I don't know why. So in that case, I've taken the start and end points.