any GPS performs as a basic computer as well - do they need any form of sensor or is it all via satellite positioning?
No sensor, for basic computer functions. So if you have multiple bikes all you need is multiple bikemounts.
Many Garmins (not only the bike-specific ones) can also do HRM and cadence if required, using Garmin's own sensors.
A typical 'computer' display - the actual data fields shown are very configurable - around 50 choices ...
you can also overlay any 2 or 4 of these on a map display ...
To me, the 'Distance to Next' is
the killer feature of GPS.
suitable roads - well a cycle option would be good for me as one of the reasons I'm considering a GPS is for multi surface exploring type rides on a MTB.
Maps - these live permanently in the GPS memory? what sort of area and scale can it store? are there proprietary limitations around the GPS you buy, as in will only work with their own, or approved, map sources?
Where auto-routing (or route-finding) is concerned - it seems to be very difficult to achieve the sort of 'intelligence' that can second-guess what a cyclist would see as a 'good' route. Although some (older) GPSs offer a lot of configurability in this area, there is no single 'right' setting that a cyclist can rely on. It's also very dependent on the maps you have installed. But auto-routing isn't compulsory - I use a GPS all the time and
almost never don't often use its ability to find a route.
Maps - some GPS can't store or display maps at all, but these days it would be hard to recommend that type as a 'first GPS'. Mostly they can store far more map than you will ever need. My (quite old model) GPS has road mapping for all of UK, France, Switzerland, and parts of Belgium, Netherlands, Germany, Italy, Slovenia and Spain - all down to street level (house-number level in the UK), plus contours as an overlay for all that area. This takes up around 1.5Gb of a 2Gb memory card, and it's easy to swap this out and put a different map in if I want.
Scale-wise - these 'vector' maps are effectively infinitely zoomable - the closest zoom (biggest scale) is almost out-resolving the accuracy of the GPS, while the widest zoom fits all of Europe on a 2x3 display.
If you want topographic mapping (better rendering of off-road features) then that takes up rather more room (and is much more expensive to buy, per area).
All Garmins can work with free 3rd-party maps, in some areas including the UK these are pretty good, and especially so for off-road stuff. All modern Garmins can also do OS and IGN mapping (at a price).
It's quite easy to swap maps around, though many Garmin maps are subject to a 'locking' restriction (map license restrictions). Garmin maps seem very expensive (mainly because it's difficult to buy just the bits you want - you may have to buy the whole of Europe, for example) - but I think they are very good.
Start/End points - your previous answer re return to home or new location indicated I could just find a location on my stored maps and click on it to be guided there. If it can do this then why would it not be able to take two points and work out the route between them for me? I do understand that I might not be getting the best out of it and I know I can plan a route via multiple points.
Yes you can do all that easily - but my personal opinion is that A-B it's just not reliable, if the distance is more than say 20 rural km. I would always want to specify a few via points to lock it down a bit. As a cyclist I view taking a wrong turn as a minor disaster. If you're looking for a Magical Mystery Tour - well, I think life's a bit too short for that, far better to use a large-scale paper map to find the best roads, then put down a waymark so your GPS can take you there.
so far I figure that the cycling specific, Garmin Edge range?, probably wouldn't be right for me as they have a lot of functionality I don't need, is that a reasonable assessment?
Well personally I don't see anything wrong with having functionality you'll never use - that's just the way modern electronic chippery works (look at digital cameras). The Edge is very much aimed at the 'step up from a bike computer' market, and is very neat on the bars. Personally I don't like the fixed rechargable battery - but many people wouldn't see this as an issue at all. If you're leaning towards an Edge you'll have to hear from people here who use it!
