Andy in Sig said:
thanks for the maps explanation: for once something in understandable English on the topic. Are you in a position to recommend which system or combination of system and mapping comes nearest (in terms of functionality rather than appearance on the screen) to having a map in your hand?
The choice is Garmin vector or OS raster, but what's best depends on what you want out of your mapping.
Are you just interested in getting to the right place, or do you want to know about the area you are passing through?
For navigation, vector is best.
Using Garmin mapping on a suitable Etrex, you get a map that contains all roads down to the smallest, so you can zoom right in and see in advance whether the crossroads ahead has a stagger on it, and whether it's 10m left or 10m right. If you get the more expensive version of the mapping, it also knows about one-way streets etc, and will plans routes for you like a car satnav. If you don't want to do that,you can just treat it like a moving map showing an area (zoomable) around your current position. You can also pan across to see stuff that's off the edge of the screen.
What it's bad at is providing any context for the roads. Pretty much all you get is railways, rivers and larger streams. It's difficult to make sense of what you see zoomed right out - picking out where the towns are for example.
There is a version of the Garmin maps that includes OS data - contours, small steams, some paths etc. I don't recommend this unless you want to use the GPS away from the roads - the extra on-screen clutter makes road navigation significantly more difficult.
Garmin Mapsource maps come as a single CD with data for most of Europe, though not all countries are fully detailed. Maps are also available for elsewhere in the world (USA, Australia etc).
For telling you about the area, raster is best.
You see contours, areas of woodland, cliff lines, paths, cycle route blobs, and everything else that tells you about the countryside on a paper map, including the areas away from the roads that are blank on Garmin vector. However the limited amount of zooming that's practical means that planning longer distance routes will likely involve a fair bit of panning around. 1:50,000 detail can also sometimes be a bit sketchy for in-town navigation.
It also requires that you use a GPS-enabled PDA or a PDA with a bluetooth or compact flash GPS. Problems with this are that PDAs are comparatively delicate, have poor battery life (~4h), and screens that are often hard to read in the sun. The end result is that you'd likely end up with it turned off except when you wanted to consult it, so no track logs, and no quicker than unfolding a paper map. A PDA is much smaller than a big stack of 1:50,000 paper maps for a longer tour though.
You can get 1:250,000, 1:50,000 or 1:25000 raster date for Britain (OS), and 1:250,000, 1:100,000 and 1:25,000 raster for France (IGN). 1:250,000 is cheap, Full 1:100,000 or 50:000 is about the same cost as Garmin vector, and 1:25,000 is sufficiently expensive that you'd buy it in smallish areas for walking/mountain biking.
I'm not aware of other countries that are available in raster formats.
For what it's worth, I use 1:250,000 paper maps (or road atlas pages) for planning where to go, and the Garmin for on-the-bike navigation.
