Got an old Edge800. Its got GB+Europe Garmin CityNav map on the SD card, all works fine.
I found talkytoaster and want to get his free GB OSM map on there for the offroad stuff.
Can the edge800 accept two maps on the SD card? It seems it needs to be called “gmapsupp.img” and I can’t find any info on how to put more than one .img file for the edge800.
Am I going to have to have 2 SD cards and swap them depending on ride?
I don’t want to overwrite the Garmin map .img file.

Just rename the img file.

Rename which file(s) to what name(s)?

Reason I’m asking here is the SD card is almost full with the existing gmapsupp.img map, so I’ve got to go get a bigger card before I can try anything. Ta.

Rename either img file. Just call it gmaptt.img or whatever. I have 6 (IIRC) img files on a card in my Oregon.

As far as I know, there’s no way of switching maps. One file name, so you’re better off with an sd card for each map – they’re cheap as chips now anyway why would you want to faff renaming each time you want to swap (granted – if you’ve got as many as 6 it would make more sense to have one card).

I’ve got to go get a bigger card before I can try anything.

The Edge will have internal memory that you can drop the Talky Toaster map into.

Garmin have some ridiculous licensing restrictions placed on their maps and if you bought the CityNav map on card it’ll be locked to that card and won’t work on if transferred to another (I bought one and came locked to a tiny, used 4Gb card). If you downloaded the Garmin map it will work off another card but is likely to be tied to your specific Edge 800.

That said, I believe that there is software available on the ‘net to unlock Garmin maps.

As far as I know, there’s no way of switching maps.

Not sure about the Edge series, but my Oregon allows the enabling & disabling of maps in Settings and I think (although I might be wrong) that you can overlay multiple maps.

As far as I know, there’s no way of switching maps

You can switch maps in the settings. I have OS and OSM maps on mine.

I thought the talkytoaster OSM maps were locked sometime around 2013 and went subscription only? Just be aware you may be looking at relatively old maps. Obviously, depending where you plan to ride this may be more or less significant, I’d be more concerned around towns and cities than BW’s etc.

talkytoaster free british isles map is 1.1GB, Edge internal memory (volume) is only 110MB total and there’s only 0.6GB free on the SD card. Definitely has the menu option to enable/disable all maps on the SD card, its just i can’t get any more maps on it.
I contacted talkytoaster via chat (great support!). Assuming the CityNav maps are locked the only way is to get another SD card for the tt maps and swap cards. Not a massive problem, one card for road one for MTB.

The CityNav map should only be locked to the SD card if you bought it on the SD card, if you bought it via download it’ll be locked to your Edge and should work from a larger card. Again I think that there’s software available to break the locking system.

FWIW I prefer the Openfietsmap version of OSM. Much less cluttered. If only they’d update the UK portion more frequently than once per year.

Im just about to try openmtbmap/velomap as an option.

Openfietsmap  is a great version, I’m leaning towards using it a bit more than the openmtbmap for offroad these days.  Openvelomap for touring though