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I'm a new user, so perhaps this is a silly question. I've noticed that the placement of roads and other items differs slightly from the yahoo map background. Is this just a problem with the alignment, or are these items mis-located slightly? Should I move streets and building tags to match the yahoo map perfectly? I'm specifically looking at about Washington, Pennsylvania, USA, between College Street and Lincoln Street. |
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No, you shouldn't move the roads just to match the imagery. The images may have had some corrections applied to them, they won't be perfect and could well be out of alignment themselves in some places. Instead you should look at all the evidence available to determine the position of a road, including GPS traces from mappers, imagery, other data sets and any other survey information. The imagery may well provide better positioning than some sources of data — low quality imports such as TIGER, for example — but that's not guaranteed to be the case. If you're not sure where the road should really be, just leave it where it is until we have better information, of whatever form. Having a road a few metres out isn't going to create massive problems, but trying to make the roads fit images when it may be the images that are wrong is just a waste of your time. |
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You can also move the background satellite imagery. In Potlatch you do it with holding SPACE and dragging the background. In JOSM you have to find Imagery offset in Imagery menu. I don't know how you do it in Merkaartor or other editors. The best solution is to find an intersection with lots of GPS traces, and align the satellite imagery with the gps traces. |
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If you are familiar with JOSM, you may check for existing GPS traces by selecting File -> Download from OSM, selecting the relevant area and activating the Raw GPS data checkbox. If people uploaded GPS traces, they will be downloaded and you will be able to compare them with the existing OSM data and the aerial imagery. 5
You can also display all the GPS traces that users have uploaded on the OSM server in the other editors like Potlatch or Merkaartor
(22 Sep '10, 19:25)
stephan75
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Along these lines, does this mean we should route roads according to actual GPS data, even if the yahoo map background has not been updated with the new roads that have been made? (i'm also a new user)
Yes, definitely.