Garmin City Navigator Maps Around The World

But using OSM would make the downloads larger, because OSM doesn't use Garmin's NT compression. When I had Here installed on my phone, the entirety of North America took some 12 or 13GB of space, compared to the 6GB+ Garmin takes.

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It may also be possible to use Garmin's Basemap which used to be installed on all thier automotive devices, and may still be. These are used by the GPS to display major roads and locations when there is no City Navigator map present for your current location

That seems unreasonably high, considering it's almost the smallest size as well. Does an off the shelf GPS, presumably loaded with local maps reflect that outrageous price?

Gamin licensees there maps from Here (https://www.here.com). I'm betting it has to do with how hard it is to map places like that. They likely charge more for the license.

Garmin has to process the maps further on their own end as they have a proprietary formatting & and compression algorithm called NT (New Technology).

Now as to why on earth the Australia & New Zealand mapset's cost of $159.99 for only 300 MB of map data as opposed to Europe's price of $99.99 for 6.44 GB of map data is anyone's guess...

Could it be that there are many fewer sales?

I can't speak for today's sales, but in the past, it seemed like Tom Tom may have been more popular outside of the United States than Garmin is, or at least was, in some places.