Ed Avis wrote on 24/05/2010 15:05: > It appears the choice for buildings is a fight between OS maps, which are > likely > derived from high-resolution aerial photos but have been simplified, and the > somewhat lower-resolution photo images available to OSM. It is not really > possible to survey building shapes on the ground since GPS isn't precise > enough, > even if we had enough mappers to walk round the outside of every building. > > In London the Yahoo photos are adequate for tracing streets, but trying to get > buildings from them is a bit ropey. Hence my feeling that the OS data is of > higher quality, even though it's clearly a simplification of the real shape. > But in other, less crowded parts of the country a semi-automated trace from > aerial photos (using the Fuzzer JOSM plugin you mention) might be a better > way. > > (Indeed, it might be fun to trace the whole country using both methods and > then > highlight differences between the two.) > > I still believe we could do *something* to get reasonably good building shapes > into the map without waiting for the man-years needed to hand-survey them all. > Even in an area which is not any mapper's particular 'territory'. The > workflow > might be to view the aerial photograph with the OS-traced building shapes on > top, > and then either press a button to import the whole area or select individual > shapes. > > Taking the lead from StreetView in my area, the shapes around are better than nothing and are good for making sense of the map. With appropriate tagging, which is trivial with a bulk import, then it becomes easy enough to have a to-do list. Areas of little interest to people will be populated adequately, and areas where people are interested, they should know from the source (perhaps even an automated note) that they have carte-blanche to improve it.
A Wiki-Map does have the danger of trying to be all things to all men, and it is interesting to see from a single source that the cyclists can produce an appropriate map different from the general. If people are really uncomfortable with the impurity of the data (in the sense of reliability not licence), then the right approach to me is to have a specific tag that is internationally agreed to be unverified/suspect and then map producers can filter or represent that data as they deem appropriate, without the map editors needing to prejudge an appropriate solution. It would also be useful to then make PotLatch et al sensitive to the tag. (BTW, it may be that this already exists, but there does not seem to be anything from my cursory look). That is not just for this extracted data, there are times I have looked at an area I know well and can't believe it does not mark a path that I know well. I would rather put the path in temporarily with a warning that it needs to be verified for exact alignment, and gets on to a to do list, than not mark it at all. I'll walk it eventually, but on a map it might get noted and verified by someone else. Spenny _______________________________________________ Talk-GB mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-gb
