OSM: Common Errors and how to fix them

On this page, I describe some common errors I found when working on OSM data and how to remedy them.

The tool of choice for all advanced edits is IMHO [JOSM].

Double nodes/ways as a result of duplicate upload of data

Sometimes people seem to upload data twice. Be it because the first upload seemed to be unsuccessfull, be it because they don't realize it... the result is the same: Lots of "duplicate nodes" as can be seen on [Matt's Duplicate Node Map].

Removing a duplicate upload

Before you can remove a duplicate upload, you have to identify it as such! What I usually do is:

• Load the area in JOSM
• Run the validator plugin

Now, if the validator shows a big number of "overlapping ways", chances are, there is a double upload of data.

Identifying a double upload

• In the validator result-window open the branch "Errors -> Overlapping Ways"
• Double-click on any entry, then hit CTRL+i to show the details of the two ways in your browser
• Your browser will load two new pages, showing the details of the tow ways
• In each of these windows click on the Changeset number

Now you see the two changesets that produce the "overlapping ways".

Here comes the crucial step: Use your brain!

Removing a redundant changeset

Once you are certain that one changeset is redundant:

• change back to JOSM
• open the search-window (CTRL+f)
• enter "changeset :" followed by the number of the redundant changeset

This will select all the data from that changeset. Now you can take a deep breath and hit DEL to remove it.

Dupilcate nodes

Don't ask me how, but some people manage to edit a piece of map and manage to put tow nodes at exactly the same position... Most probably this happens by automated upload of data that is derived from other sources (e.g. extract streets from a source, convert and upload to OSM, then extract landuse from the source and upload -> points that are in both will be created double).

Identifying duplicate nodes

Simply run the validator plugin and check under "Errors".

Removing duplicate nodes

Once the validator has identified the double nodes, you must make sure that they all come from the same problem (root-cause). For that, double click some of the entries and check where they come from and wheter they can simply be merged.

If you are certain that all the nodes in one Error categorie of the Validator can be fixed by merging them, then select the categorie in the Validator window and click on "Repair".

If you are not 100% certain, fix one node at a time:

• Double-click on the error entry in the Validator window to select both nodes
• Right-click on the entry and select "Zoom to problem"

Now yo can examine the nodes and see what the problem is. If the nodes can be merged, then click on "Repair" (or hit "m" - merge).

End of way near other way

This error typically happens when people don't use the Validator plugin (or don't care about its messages) when creating new streets/ways. What the error means is simply: Two ways are almost connected, but not completely. Usually, less than a meter is in between. Optically, on a rendered map, this is not a problem. Every human will assume the streets should connect and base his/her routing on this assumption. Routing-Programms (e.g. car-navigation systems) can not make that assumption and may not be able to find a (good) route!

Identifying unconnected ways

Run the Validator plugin. Under "Warnings -> End of way near other way" all the candidates for such unconnected ways are listed.

Unfortunately, there is no quick way to fix them. You will have to do the following steps on each of the problems:

• Double-click the entry -> both ways are selected
• Right-click the entry and select "Zoom to problem"
• Inspect the situation and use your brain (or knowledge of the situation in the field) to decide if the ways should be connected or not.

If you think, the ways should be connected, then use the normal JOSM tools to correct the situatin. Most of the time, one street can be "glued" to the other: Select first the end of the street you want to move a bit, then select the node you want to glue it to (aka: select source first, dest second) then hit m to merge them.