OS Maps

IanForrest said:

I confess i am not really sure what you mean by OSM.  Where do I find those?  Do they give similar detail to OS maps?

OSM is Openstreetmap. Your 830 already comes with (versions of) these maps.

IanForrest said:

What do the other, much smaller, files actually do?  Some are SUM files and there is one that is a GMA file, an XML file a BIN file and a Text document file. 

The maps need to be in the "\Garmin" folder.

The *.img file is the actual map file. I believe the GMA file is a license/lock file. I don't think the *.txt or *.bin files (if they have the same name as a *.img file) do anything. They might be related to incomplete downloads.

I believe the Ordinance Survey (OS) maps are locked to the microSD card or the device. That is, I don't believe you can just copy them around and get them to work.

Many people in the UK prefer the Ordinance Survey (OS) maps.

The OSM maps have a varying degree of quality, depending on location. It wouldn't surprise me that the OS maps were better.

I like the OSM maps fine (I'm a fairly-regular contributor to updating them).

One advantage of the Garmin devices is that you can install other maps.

Ah, ok thanks.  I guess that is a licensing thing.  But v irritating since I bought the license!  Won't make that mistake again.  They are v expensive.

You aren't the first person to get hung up by this. It's the choice of the Ordinance Survey (the provider of the map).