How do I reference GeoJSON data easiest in JOSM?

Hello, everyone! I recently took the plunge after 1000 or so changesets using iD to finally start trying out JOSM. I can definitely see how it’s more powerful though definitely a bit of a learning curve.

What I’m trying to figure out is how to do something that I find relatively easy in iD, of referencing outside information sources while editing. I’m not trying to import it directly, just look at the data in various places.

For example, say I want to look at the (public domain) MassGIS data on Massachusetts libraries. This is hosted on ArcGIS, and I can get the GeoJSON by downloading

In iD, what I can do is go to the Map Data tab on the right side, choose “Custom Map Data”, and put in that URL. Then all the points show up as magenta circles, and I can click them to look at the data while I edit. So I might use it as one source to figure out where the library is if it looks like it might be in the wrong spot (I think some in Massachusetts were imported long ago and have since moved, and I’ve fixed a couple of those), or to get a library’s web site to include that in OSM or so just look at for more information. I’m not doing any sort of “importing”, just using it as one additional source of data to reference.

I’m trying to figure out how to do the same sort of thing in JOSM. There’s a “Data” menu with “Open custom URL”, but that looks to be something different entirely. The main thing I think I’m supposed to do is to choose Open Location in the File menu and open that GeoJSON URL as a new layer. But once it’s in the new layer, it seems really tough to actually use. The points are really small and can be hard to pick out (as opposed to iD where the circles are bigger and can be easily seen at any zoom level), and I have to switch to it as the active layer in order to click the point and see its properties. So it looks like I need to switch to the GeoJSON layer to look at something, and then switch back to my “main” OSM layer in order to use the information. And while in the GeoJSON layer, I need to be careful to not accidentally move or edit anything, since JOSM is treating it as a data layer like any other I might want to modify.

So I guess I’m just trying to figure out if I understand the process right, and if there’s anything I can do to make things easier. Is there a way to mark a layer as “read-only”? Is there a way to look at properties on one layer while modifying another? Is there a way to make the points more noticeable than the tiny cyan squares which can be hard to see against some backgrounds? I’m guessing there’s a plugin or two to help me, since there look to be a bazillion of them, but I’m not even sure what the term is for what I’m looking for.

Thanks for any insight you can give. I was hoping that JOSM would make things easier for if I wanted to reference multiple sources, and to use some bigger files than I could manage to load into iD, and I’m guessing that it can once I’m used to it, but tips for how to most easily switch and handle the various layers would be appreciated.

I have some hints but no full solution for you:

Loading the GeoJSON into a separate layer is the way to go. This also makes sure that you don’t accidentally upload the whole file as objects into OSM.

There are keyboard shortcuts Shift+Bracket Open and Shift+Bracket Close to switch the active layer. For me the shortcuts didn’t work due to my keyboard layout. You can change all shortcuts in the JOSM settings.

Also there are shortcuts Alt+1, Alt+2, … to toggle layer visibility on and off.

The layer visualization can be changed with Styles in JOSM. I couldn’t find one to make the nodes in external data layers bigger. In theory you could create your own style, but that would be quite an advanced task.

Just to give an update on some other things I’ve tried and found helpful:

  • I can select all the points (Ctrl+A), then bulk edit the tags. So I can rename “NAME” (from the GeoJSON data) to “name” which will have JOSM show the points with names next to them. Basically in general, I can take advantage of the fact that the layer is editable to make the data look more like OSM tagging to influence how it shows up.
  • I can search for particular points, and then even add them to the To-Do plugin to allow for systematically reviewing each of the points.
  • The “HiDPI” map paint style helps makes the points just a bit bigger.