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I am mapping in Central London (where I live) and have noticed a very large number of inaccuracies. I have been trying to fix these.

However it is clear that nothing short of moving almost every building and road to make their position more accurate will do. It is clear that all outlines of roads, buildings, etc have come from some imagery not available in the editors, and not aligned with OS's data. The GPS traces in the area are absolutely diabolical, ruling that out as a source.

My plan is to use OS's Open Data to get road and building-block outlines to match up with OS. As it stands, almost nothing where I'm mapping matches up with this data, but the data itself is very much not consistent with 'real-life' nor even with itself.

It seems the most sensible option to me to use OS to do this. But are there any thoughts, critiques, or problems that should be pointed out before I undertake this task?

To clarify, I don't think I will be stepping on anyone's toes by moving buildings around slightly. I have already added so much data in my area that it is almost entirely my own work... except for the overall building outlines and road paths, which are inaccurate!

asked 12 May '20, 13:11

owenward's gravatar image

accept rate: 0%

edited 12 May '20, 13:41


Have you verified that OS Open Data is correctly aligned in your area? It could be off for any number of reasons and it would be a shame if you spent all this time moving all buildings just for someone else to have to move them back at a later time. Never trust something blindly just because it is issued by the government (or a former arm of it)...

(12 May '20, 13:20) Frederik Ramm ♦

No I haven't verified this... not sure how I would though.

I trust OS because I have used their Master Map which is extremely impressive. It even has an accurate outline of my grandma's garden shed. Master Map is industry standard and used for all professional uses that I know of (research, planning, etc). My assumption is that OS Open Data outlines are inherited from the Master Map, in which case they would be more accurate than anything else available. But I may be wrong on that!

(12 May '20, 13:27) owenward

See also , which this conversation seems to be related to.

(12 May '20, 14:57) SomeoneElse ♦

There are many GPS traces available in London. Unfortunately many of them only as unordered points but some intersections have a pretty good coverage of lines (e.g. at Piccadilly Circus).

I used these traces to check the offset of "Esri World Imagery (Clarity) Beta" - which is perfectly aligned (instead of ""Esri World Imagery"!) - and then compared it with OS OpenData Streetview. Both imageries match.

So I guess moving building outlines in London according to this imagery is fine. If the offset is large enough, of course. Otherwise just don't bother. However since this sounds like a larger bigger task you should discuss it with the local community first.

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answered 12 May '20, 14:48

scai's gravatar image

scai ♦
accept rate: 23%

edited 12 May '20, 14:49

Given that there is perfect alignment at Piccadilly Circus, does this mean there will be perfect or near perfect alignment nearby? E.g. within a mile radius?

(12 May '20, 16:28) owenward

That depends heavily on whether the terrain is even. On hilly terrain the offset may vary significantly whereas on even terrain the offset should stay the same.

(13 May '20, 07:20) scai ♦

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question asked: 12 May '20, 13:11

question was seen: 1,354 times

last updated: 13 May '20, 07:20

NOTICE: is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum