OpenStreetMap
I saw on the OSM-talk mailing list that Osmose is now available for North America. This is a great tool for finding issues with existing OSM data, and the interface is chock-full of helpful links and functionality. I was able to get off the ground almost immediately, starting from a position of no knowledge about Osmose whatsoever.
Most of the errors it finds are described pretty well, and the links to the OSM wiki help fill in most of the blanks. I was able to fix quite a few little problems around my city.
One error that I haven’t been able to figure out is one of the multipolygon-category errors: “Should be polygon or part of multipolygon”. The wiki describes it thusly:
Class 4 “Should be polygon or part of multipolygon” : the nature of the way indicates that it is a surface, the way would be a polygon or of a part of a multipolygon as outer role.
It may be the translation that is making it difficult for me to parse that. The places I see this error are almost all buildings, but not multipolygons. I don’t really see any obvious commonalities between them, or differences between them and other nearby similar buildings. In one case, the error references a landuse=residential.
Can anyone shed light on this error? Can these examples be marked as false positives, or is there some aspect of these ways that trigger the error?
Discussion
Comment from maxerickson on 13 April 2015 at 23:02
http://www.openstreetmap.org/way/208009706 is not a complete area and redundant with the larger building it overlaps (not sure which this report is based on).
http://www.openstreetmap.org/way/184684683 looks like another extra fragment.
http://www.openstreetmap.org/way/102238692 overlaps itself on the top left corner.
http://www.openstreetmap.org/way/330790724 has an extra node at the “3rd step down” on the right, so it doubles back on itself.
http://www.openstreetmap.org/way/256128927 doubles back on itself too, the top right corner of the top bump out.
http://www.openstreetmap.org/way/304040452 doubles back on itself on the top left corner.
http://www.openstreetmap.org/way/303570359 has two nodes that are very close to each other on the left middle.
http://www.openstreetmap.org/way/330875894 doubles back on itself by the intersection with the park and bike path.
I left them all alone so you could easily go look at them.
The JOSM validator flags the doubling back as Self-intersecting ways, that can help in finding them (though it often doesn’t help in pinpointing the error, so you just have to look for the mess).
Comment from jgruca on 14 April 2015 at 03:26
Thanks so much!
Looking at these same ways in JOSM and using the validator there made this a lot easier. I had been looking at the errors in iD on a computer I did not have JOSM installed. Finding the weird geometry issues was a lot harder there.
The error message would have been more helpful if it indicated that inconsistent or self-overlapping areas would trigger it. I guess that was the “Should be polygon” part – these errors caused the areas to no longer be polygons.
Again, thank you for taking the time to look at those, and to give such detailed explanations of what was going on.
Comment from maxerickson on 17 April 2015 at 17:14
I had forgotten about it when I wrote the earlier comment, but right clicking on an error in the JOSM validator and selecting “Zoom to problem” will do just what it says.