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I received the dreaded "multipolygon not closed" error message recently. There was apparently a "gap" somewhere that prevented the 105-member multipolygon I was working on from compiling as it should. Try as I might I could not locate the error or gap or whatever the problem was by using any of the built-in functions of the Relation Editor. I was able to resolve the problem but the Relation Editor wasn't much help.

There is a function in the Relation Editor that is supposed to allow one to visualize, even to highlight, such a "gap" and perhaps it did that, but it never told me what sort of gap it was. I was looking for a place where I had forgotten to join two ways. That is the usual reason for such an error message. As it turned out, I had forgotten to change the role of a large way segment from inner to outer. But neither the message nor the Relation Editor UI gave me that critical piece of information.

The only readable mention besides patch reports in the JOSM Wiki about "zoom to gap" I was able to find was this: "When fixing larger (route-)relations it would be very helpful if there were buttons within the Relation Editor for jumping to the next or previous gap in the graph." I would add, and then add to the documentation a short description of how to use those buttons. A definition of exactly what a gap is would also help.

Taking a look at the Relation Editor dialog box on this page, we can see three columns in the the Members section at lower left. There are explanations that help me understand what Role and Refers To mean but what about the third column? I'm sure it has a useful function but I cannot determine what that might be. Also, on the far left there is a Sort button. Press it to sort the Members, Press it again to sort them in reverse. But what is the sorting based on? Moreover, why would one sort them in the first place?

The Relation Editor is a powerful tool that is, IMO, really not documented very well. Reading the Help pages is sort of like listening to a hundred TV News reports about a war. The overall story about how to use the tool effectively is hidden within a thousand small stories.

I'm not complaining about the tool itself or the people who wrote the code to implement it but I need to learn how to use it more effectively. Is there anyplace where this is all written down and explained?

Relation Editor window

asked 28 Feb '15, 10:43

AlaskaDave's gravatar image

AlaskaDave
4.7k7399153
accept rate: 14%

An alternative (not JOSM and works only works if the relation is already uploaded): With http://ra.osmsurround.org/analyzeRelation you can see the gaps easily on a map (markers at all ends).

(01 Mar '15, 13:09) aseerel4c26 ♦

I am not sure if I am understanding your problem correctly, but will try:

@"what about the third column": see Help/Dialog/RelationEditor: "on the right information about neighbor ways' connections useful for consistency checks like checking that the members of a multipolygon form closed ways or that a route is a complete line without missing some ways in the middle."

This only works in a useful way if the relation members are sorted. You can do that either manually or with the button which you have discovered. If I remember correctly: If you just press the button it sorts all the members. But you also could select only a part of the members (in the "Members" list) and then press it - then only those will be sorted. What the sorting does? From what I saw in the past it tries to sort them in a way that they are in an order which allows you do jump from one member to the next member. Meaning: the end nodes of a member way will be shared with the previous/next member way in the "Members" list.

The red points (see the "third column") mean that there is no connection to the prev/next member.

Addition: Apparently you were quoting from (among others) ticket 7168 ("Add a "jump to gap" functionality to the relation editor") – which has been implemented if I read correctly. I think I never used this function myself. Okay, I think I have found it: It is accessible via a right click in the "Members" list. But seems to only work with sorted members, it just searches for the next red point in the "third column". /Addition

Just a general note: I think it is a good practise not to blindly click the sort button when you encounter a relation which appears to be slightly unsorted. At least check which type of relation it is, maybe check the history for comments.

And one more: Once you've understood the relation editor and tried a few times, please help to improve the JOSM help page. It is a wiki, you do not need to be a programmer to change it. Sign up, log in and edit.

The JOSM help should be the "place where this is all written down and explained". You will find a bit also at e.g. https://wiki.openstreetmap.org/wiki/JOSM/Advanced_editing#Relations but that is more basic.

permanent link

answered 01 Mar '15, 12:15

aseerel4c26's gravatar image

aseerel4c26 ♦
32.4k17241554
accept rate: 18%

edited 01 Mar '15, 20:21

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Thanks asseerel, that's a help. I will try to educate myself more fully as I go and, should I gain enough experience and understanding, would definitely add some clarifications to the Wiki.

I will also give the Relation Analyzer a shot tomorrow.

(01 Mar '15, 13:14) AlaskaDave

Hi Alaska Dave, why going into the Relation Editor ? If you use JOSM, the build in tool validations with warnings; makes perfectly clear with yellow dots where the mistake can be found.

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answered 28 Feb '15, 15:19

Hendrikklaas's gravatar image

Hendrikklaas
9.0k187219366
accept rate: 5%

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Not really. In a a large relation with many members the yellow overlay is not enough to pinpoint where the error is. Nor do the yellow lines or error message indicate what the error is. In the case I mentioned the polygon was indeed "not closed" but it was because an inner member should have been an outer. A better error message would have saved much time.

(28 Feb '15, 23:45) AlaskaDave

Okay, looking at the yellow dots or ways solves the problem most of the time.

(02 Mar '15, 15:24) Hendrikklaas
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question asked: 28 Feb '15, 10:43

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last updated: 02 Mar '15, 15:24

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