How can I add layer A to layer B in JOSM without doubling the objects I had in layer B before and are also in layer A? And having the objects that are attached in layer A attached afterwards also in layer B?
There is a button: Merge this layer into another layer. I think that’s what you are looking for.
Thank you, Jo. I retried with Ctrl+Shift+M and found out the following: It works withoud duplication as long as also the keys are identical. But I’ve added a key in my .osm-File. So the highway downloaded from OSM gets copied over the one existing in my file, so I got two highways with the first one a key more. Isn’t there a way of telling JOSM to NOT merge objects that only differ in keys?
In this question you ask the opposite of what was requested before.
The default behavior in JOSM is to merge two objects to one, if they have the same positive id and one of them is modified and the other unchanged.
To accomplish without merging, you could Ctrl-a (if you want all objects), Ctrl-c in the source layer, then Ctrl-v in the destination layer.
Of course, it’d be best to have the todo plugin installed and then verify all these objects with it one by one, with help of the todo list.
Alternatively, you can give those new objects a tag like created_by=whatever or odbl=new, then search form them until all are either merged or you verified no merge is needed. created_by/odbl will be discarded before upload, so they are quite harmless.
An alternative to that is to create a MapCSS style which shows objects tagged with those tags differently at all zoom levels. That’s what I did before we had a todo list plugin.
You can also create a one click preset, to remove these created_by/odbl tags. Add a button on the toolbar for this preset and this becomes very convenient to use.