This is a great site if you own a Garmin GPS: http://garmin.openstreetmap.nl/ . It allows you to get recent map data for other countries onto your device.
You have the option of simply selecting a country and hitting the download button, or of creating a custom map. Selecting by country is the better option, as each country is already pre-packaged and available for immediate download. Creating a custom map can be quite time-consuming, and after you've tinkered with the tile selection for a while you'll press the download button and discover that you'll now be required to wait while their servers assemble the custom map for you - a process that can take 24 to 48 hours on one of their popular days (they were popular when I tried to make a partial map of France in April 2014, but in May 2016 the map queue was empty and my map was generated within about five minutes).
Downloads are large: in the neighbourhood of 1GB zipped for a European country.
You'll be offered a set of files:
They're all quite large. I generally take the osm_generic_new_gmapsupp.zip because it's the one that's meant to be decompressed and written straight to the SD card for the device, whereas the others are for if you're on Windows and/or you want to tinker with the maps first.
Unpack osm_generic_new_gmapsupp.zip and place the resulting gmapsupp.img file into the /garmin/ folder on the SD card you intend to put in the Garmin GPS. I'm sure there's a size limit on how big an SD card the Garmin's will take: my old Garmin nuvi 255W has been fine with an 8G SD card, which is more than large enough for most purposes: the unpacked gmapsupp.img for France was 1.4G in 2014, Italy is 0.8G.
Apparently - and reasonably enough - you can have multiple *.img files on recent devices, and thus have multiple countries without having to resort to custom maps. But older devices will only recognize one file with the exact name gmapsupp.img. To my considerable surprise, it appears that my 2010 Garmin nuvi 255W is in fact able to hold multiple .img files in its little brain, suggesting that when they say "older devices" they really mean OLD.
Why Garmin Isn't Worried
Garmin charges a fair bit for map data: for France, I would have had to pay them $70 for an SD card with Europe on it. Given that I paid $100 for the GPS complete with North American maps, this seemed a bit much. So I went the self-service route. But Garmin isn't worried because:
- this is kind of a pain in the ass to use
- the map data is fantastically uneven depending on how active Openstreetmappers have been in the areas you're going to (it ranges from significantly better than Garmin's to essentially non-existent, it's quite amazing)
- even if the data is good, the on-the-fly car routing isn't very good: you really have to pay attention and double-check that it's not sending you through Nantes on your way from Paris to Calais (if you don't want to look at a map, think "massive and absurd detour")
- sometimes Openstreetmap supplies too damned much information ("this is a field of grass", "here is a water fountain"), and that really clutters up the presentation on the GPS screen
Despite which, it served me quite well through a two week vacation in France.