On Thu, Feb 12, 2009 at 02:07:02AM +0000, LeedsTracker wrote: > > Mapping an area after it has been traced is: > > > > a) almost as much work as without the tracing (you still have to go > > down each road to look for missed features) > > b) very unsatisfying because it doesn't look like you have achieved anything > > Just wanted to follow up on this point. > > I've been mapping bits around Warrington recently using Yahoo imagery, > as there is no coverage around areas I know, and there are big rural > areas round there with little mapped. > > Do others feel the same as Brian? I could understand why. > > For now I'm leaving roads alone and adding fields, woodland, streams > etc via Yahoo imagery as these are harder to map by GPS survey.
It used to be the case that people would trace over aerial imagery and use the awful convention of highway=* (an actual classification, not “road”) and name=FIXME, and they got rendered normally, so it looked like an area had good coverage at a glance. With highway=road being used, I think the situation is a little better. At the last Manchester mapping party, we encouraged people to trace Yahoo! imagery beforehand (and many did, thanks!). I personally didn’t find it an advantage, and one of the areas I surveyed wasn’t fully covered anyway, but some other people did say they found the traces useful. I’ve tried tracing an area, then mapping it later. I can’t say it has been an advantage then either. I probably won’t be tracing areas I’m likely to map at some point in future because it’s more effort than just mapping. If someone else traced it, I wouldn’t mind too much since it doesn’t generally make my effort harder. (What I do mind is when people apparently trace from aerial imagery, and name the roads from memory and get it wrong. Grrr!) It is less satisfying, but even data from tracing can be useful, and if someone else is putting some effort in to get useful data I’m not going to actively discourage them; it’s not just my map, and my work. A possible advantage for tracing roads is in an area with few active mappers. Someone could trace roads, then someone could go out and collect street names, classifications, etc, without even needing a GPS device. Having said all that, I do think concentrating on landuse and large land features is a much more efficient use of aerial imagery, since Brian is correct, you have to go out and map it anyway. Simon -- A complex system that works is invariably found to have evolved from a simple system that works.—John Gall
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