Conflict

JOSM locally manages copies of OSM objects. It loads them from a file or downloads them from the OSM server and keeps them in memory. If you update a map with objects or modify their tags you are working on copies. The reference object is still kept on the server from where other users can retrieve it and where other users can send their updates to.

This means that you don't own the objects you are currently working with, you still share them with others. If you exchange your local objects with the server your version may clash with the version somebody else sent in as update. JOSM does its best to hide these clashes from you but sometimes it can't resolve the differences between two versions automatically. In this cases it creates a conflict.

A conflict is a difference between two versions of an object which JOSM can't resolve automatically.

Conflicts when downloading/updating

If you download objects from the OSM server into an existing layer, the objects from the server might "collide" with objects already present in the layer. Often, JOSM can handle these collisions automatically but sometimes this isn't possible. Here's an example:

1. You've downloaded a node with id 1 from the server whose name tag is set to My name.
2. You edit the node and change its name to Or is it this name?. In the meantime another user downloaded the node too, changed its name to That's the name, and uploads it.
3. You select the menu File->Update data. The version of the node retrieved from the server will have a tag name set to That's the name which collides with Or is it this name?, the name you've been setting.

JOSM can't resolve this automatically. It creates a conflict. Typically JOSM displays an error message as follows:

Conflict when uploading

If you upload objects to the OSM server, they might "collide" on the server with updates provided by other mappers. Sometimes, JOSM can handle these collisions automatically. If, for instance, you try to delete an already deleted object JOSM will sillently skip deleting and it won't bother you with an error messages. In most cases, though, JOSM can deal with them automatically. Here's an example:

1. You've downloaded a node with id 1 from the server whose name tag is set to My name.
2. Another mapper downloads the node with id 1 too, assigns it the name That's the name, and uploads it.
3. You change the name to Or is it this name? and upload to the server.
4. On the server, you're upload collides with the upload from the other mapper.

JOSM can't resolve this automatically. It creates a conflict. Typically JOSM displays an error message as follows:

Conflicts when merging

See also

• Conflict Dialog - You can use the conflict dialog to resolve a conflict