OpenStreetMap
Re-drew sections of the A27 along the South Coast which I can see via Yahoo tiles as it seems to be out by about 15-20'.
However, there are large sections that I can't see due to lack of low-level mapping or clouds. So, if there's anyone along the South Coase available to go over the route with a GPS, you'd probably be able to correct it all fairly easily
Cheers
Mike
Discussion
Comment from njd27 on 22 August 2008 at 10:14
For what it's worth if the aerial mapping is out by 15-20' then it's likely to be the aerial mapping which is aligned badly - particularly in areas where there aren't many features. If you view all the GPS tracks for the road and take an average that is far more accurate generally.
Comment from LivingWithDragons on 22 August 2008 at 14:51
It's probably been done with a GPS and, as njd27 says, the aerial photography out.
Also not everyone uploads their GPS tracks, some people just open them locally in JOSM.