Matthias Meißer wrote:
Of course we know, that using just Bing, is just the #2 choice for adding details to our database and that survey is what we all really like. But in this case, we believe, that it is a good compromise (see hints in Wiki). Currently there seem to be no definitive answer if this technique is right or wrong, maybe we can decide on this when years passed and we can take a look back. So for now, let's just do what we are good at: Create together a real good map :)
As Nick has said, we need to be a little careful here. It's one thing for someone who's familiar with an area to add in features using the Bing overlay to help them, but something else entirely to add features to the map based only on what it looks like from overhead. The things that are useful to know about countryside roads tracks and paths are things like access rights (Am I legally allowed to drive down there? What about cycling?) surface (OK, I'm legally allowed to cycle down there but would I have to carry it most of the way?) and all of the points of interest (gates/stiles/shops/pubs etc.) that you can only get details of by actually going there.
If you don't add any of those things you end up with something that's a poor facsimile of a Google map. In the UK at least, Google recently replaced third-party map data with their own, derived by exactly this method - and while it's fine at navigating from town A to town B via major roads it's a bit poor for anything else. As an example, on a Google map go to 53.186133, -1.151462 and zoom out one notch. Other than the A and B road that you can see, none of the "roads" that Google shows actually are.
Another potential problem is alignment - both GPS traces and imagery might give odd offsets in hilly countryside (and as towns tend to be built on the flat bits, this might not be something that town mappers are familar with). Some Bing imagery is wildly offset (see for example http://www.openstreetmap.org/edit?lat=32.7411&lon=-16.6912&zoom=14) but it's often possible to align it better with a combination of multiple GPS traces and the local knowledge of having been there. It can also be fairly out of date - if you believed Bing, you'd think that Britain still had a coal mining industry.
Perhaps a better approach would be a combined one of adding features from Bing etc. AND then going out, getting a bit of fresh air and collecting all the useful details that you can't get from an aerial photograph? Sure some things (woods, lakes) aren't easily accessible on all sides and aerial imagery is really helpful filling in the gaps that you can't get to but things like "who owns that wood?" and "is their permissive access?" can usually only be found out by going there. Adding things in areas that are neglected locally rather than miles away means that there's more chance of a local OSM community maintaining the data once added - it won't turn into some zombie representation of how things were whenever the Bing aerial photos were taken.
Finally, please don't forget to put a "source" tag on every remotely edited object so that when someone comes along later to try and reconcile multiple sources of data they have at least got a chance of working out what came from where.
Cheers, Andy _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
