Unconnected ways and other data quality issues

Posted by amm on 12 September 2010 in English (English)

Increasing numbers of areas in OSM are starting to become "complete" or at least have a good coverage of the basic features. With this, the focus in OSM imho should increasingly move more towards "maintanance mode", ensuring that our data remains at the level of quality and up-to-dateness we pride our selves with.

So far, the majority use of OSM has probably been in webmaps and bitmap tiles, as it is a rather forgiving application with respect to data quality. Other areas that OSM is starting to push into, particularly routing, are less so. One particular aspect that is obviously very important for routing (and other applications), is connectivity or network topology. I.e. saying if one way is connected to another and if it is therefore possible to travel between them.

Unfortunately OSM seems to have a bit of a problem with connectivity and a surprisingly large number of roads and footways are drawn to end close by, but don't share a common node, i.e. meaning they are not connected. Luckily someone (was it Pascal Neis?) has made a great tool available through Geofabrik's OSM Inspektor to highlight all the roads and paths that end close (less than 1-5 meters) to another road or path, but aren't connected.

As you can see from the screen shot above, there are many of these nearly connected ways that need fixing! So let's all try and get those nearly connected ways connected and remove those red dots from the map! Head over to the OSM-Inspektor routing view and start fixing! The routing view is now available for all of Europe after only being created for Germany in the past.

Keepright, another great QA tool, between, has a similar check with its "Almost-junctions" check, and indeed several more really useful checks! So another good opportunity to fix those bugs.

As always, with any automated quality assurance tool, there will occasionally be false positives, where the way truly does reach very close but is not connected, as there might be a wall, fence or a 1000m drop preventing you to get from one way to the other. So please be careful and let the usual commen sense prevail when fixing these issues.

Comment from emj on 12 September 2010 at 14:42

At first glance the routing tool didn't seem very good but I did find lots of possible mistakes when looking on red dots, most of them weren't very obvious and will need on ground checking..

Would be great if you there was an easy tool to ask the people who made the mistake if they believe it was an error or if it the roads are really connected.. I guess I can just manually mail them instead.

Comment from Pink Duck on 12 September 2010 at 16:18

There doesn't appear to be a means of saying that the spots should be ignored because of being false positives like the KeepRight site can do.

Comment from amm on 12 September 2010 at 21:45

@emj, Yes as mentioned, there are going to be some false positives, but my impression has been that the fast majority of the <1m reports, I'd be very confident that they are truely bugs. For example, if you look at,unconnected_major2,unconnected_major5,unconnected_minor1,duplicate_ways it is kind of obvious that this person hadn't realised that ways need to be connected and one can simple connect them without too much worry about false positives.

@Pink Duck, yes it would be nice to be able to mark false positives, but it in a fully automatic reporting that gets rerun every day or so, it is hard to keep track of which errors belong to which "ignore". However, I think it supports the "noexit" tag on nodes for ways that aren't connected.

Comment from amm on 12 September 2010 at 21:51

Oh, silly html parsing. it cut of the <1m in the above comment. so lets try again:

Yes as mentioned, there are going to be some false positives, but my impression has been that the fast majority of the <1m reports one can be fairly confidant that they truely are bugs. For example,unconnected_major2,unconnected_major5,unconnected_minor1,duplicate_ways it is quite clear that the mapper hadn't realised that ways need to be connected and it is imho quite safe to simple connect all of them without too much worry of false positives. But yes, in other areas it is not as clear, and one should always err on the side of caution.

Comment from emj on 13 September 2010 at 12:13

Yes, for major roads it's extremely useful but parks is a mess, all those small footways leading nowhere.. :-) I find the most errors where lots of people have edited.

Comment from mihaiile on 16 September 2010 at 09:55

this tool is great, found some red dots and duplicated ways on my area, corrected them all, let's hope the next update removes those nasty red dots from my area!

Comment from firstvariation on 23 September 2010 at 18:00

This is a wonderful tool, very easy to use, thank you !
And, I needed to be educated about the "noexit" tag.

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