Map-Making Program

[vtk]

Would it be possible to download only sections of the OSM map data? Like the PA area? If the whole thing is 21 gigs, then this must be nothing.

Yes!

Downloading an area the size of Pennsylvania will probably require the use of a website that provides extracts of specific geographical areas on a regular basis.  It is also possible to use the website or API to download very small chunks of the map, or use the XAPI (through one of several third-party servers) to download chunks covering small cities or rural counties.  XAPI also provides the ability to (for example) only download roads, by specifying you only want objects with a highway= tag.  If you have to download your area of interest in multiple pieces, you can load the files in JOSM, which will appear as separate layers; you can then merge them and save the merged layer as one big OSM file.

See: OpenStreetMap Wiki: Downloading Data

[Roadsguy]

Would it be possible to download Potlatch 2 to my computer and use it to edit a small .osm file?

[vdeane]

I'll have to try making freeways with these then.  It would be great to have map tiles of fictional routes.

[Dr Frankenstein]

Would it be possible to download Potlatch 2 to my computer and use it to edit a small .osm file?

That or one of the many other editors available.

[Roadsguy]

Well, does Maperative work like P2, or do I need to modify the map code manually?

So if it is possible to use P2 offline for my small .osm file, then how?

[vtk]

Potlatch is designed to work directly with the live map via API, not external .osm files.  It can probably be modified to work with external files, but I think this would require compiling your offline copy from modified source code.  Richard Fairhurst is the lead developer for that, and he's fairly active on the talk@ mailing list; he would know what modifications are required and how much of the necessary work has already been done.

[Roadsguy]

Oh.

Well, what about Maperative? Does it work like P2 or do I need to manually modify the code?

[vtk]

I had not been aware of Maperitive before.  Looking at it now, I'd say it appears to be an easy way to render maps, but it's not an editor. 

I think it's worth the effort to learn to use JOSM.  You can even make it display aerial imagery in the background like Potlatch does.  The hardest part is remembering which mode you're in, because that affects what happens when you click the map, and finding some UI elements to which the documentation refers.

If you really want to use Potlatch to edit fictional maps, you can set up and run your own OpenStreetMap database, import OSM data for the relevant areas you want to edit, and then run an instance of Potlatch configured to talk to your own database instead of the real OSM API. 

I also wouldn't count out the possibility of support for external file editing in future versions of Potlatch, as its developer really doesn't like JOSM and may sympathize with this use case.  He does this in his free time though, so ask politely and don't push it.  Or better yet, volunteer to help with the coding...