I am participating in the MapRoulette cleanup, and often run into strange “orange rings” on ways (I use Potlatch). Occasionally they are isolated, an example from my area can be seen here. At other times there is a whole group of them. They seem much more common either on or near non-highway ways … administrative boundaries or power lines.
When they cause a loss of connectivity, is it safe to simply delete them and join the segments?
Many thanks.
The orange rings are as far as I know “duplicate nodes” I.e. two identical nodes on top of each other.
As ways are only considered to be connected if they share the same node id, duplicated nodes do usually lead to a loss of connectivity and can be merged to fix that. However, if the duplicate nodes come from one node being part of a road and another from being part of a admin boundary, then you don’t necessarily want to merge them.
In case of the whole group (at leas in the case of the US) of duplicate nodes, it is usually caused by duplicate ways. TIGER data, which is where most of the data in the US came from originally was imported county by county. However, ways at county boundaries were not correctly connected or processed during the import. Often, roads from one county import extended a little into the other county. Thus at the county boundaries, there are often roads that were partially imported from both county datasets, leading to overlapping ways.
If you move one of the “orange rings” in a group, you will often see that there are two ways on top of each other. In that case, you want to split the roads at the point where they start overlapping, delete one of the duplicate sections and then join the roads together again to ensure correct connectivity.
With respect to power lines, you should probably just delete one of the duplicate nodes, where they are unnecessary. Power lines and highways aren’t “connected” and thus shouldn’t really share a node, so merging of nodes would be the wrong thing to do.
I think the nodes of power lines should be placed where the masts or poles are that support the power lines.
Many thanks for your helpful comments. The MapRoulette project is an attempt to harness the power of the community to clean up the TIGER import mess … plus the messes made by careless on-the-ground mappers (some have never heard of connecting ways :().
True - but newbie mappers will never hear about connecting ways unless someone tells them! For some people (who use the data for routing, perhaps) it’s “obvious” that ways that are connected on the ground should jon on the map too. For some people it just isn’t, and the only way they’ll find out is if someone politely tells them why it’s important that roads join.
I was careful/lucky (take your choice!) when starting out.
After my first mapping I posted here asking for comments: New to OSM, and user t-i was kind enough to warn me that:
He also told me how to do so. My belated thanks!!
Unfortunately the OSM documentation does not seem to emphasize (I may have missed something) how important it is to join connected ways.