I am using the basemap in ArcMap10 to create a shapefile of hand digitised polygons based on building outlines.

However, when I change the basemap projection to Brit Nat Grid, it does not line up with the OS building polygons that are also Brit Nat Grid. No matter what course of transform/project/tool I use, I cannot get the two to concur


Assuming you are using Bing aerial for digitizing: Those aerials do not have to align with Biritish OS data perfectly.

It is up to bing to georeference their pictures and eliminate effects from photography not perfectly orthogonally more or less good.

I assume that OS has far better data sources than bing. So you better digitze from them.

  • Hmm, I guess you're right. It is very difficult to get properly orthorectified imagery for free for the part of the UK that I am studying. There seems to be no way but to use basemaps on ArcMap
    – Sam
    Aug 1 '13 at 12:41

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