Hi Howard:
Although I have done a lot of travel with the autorouting Garmin GPSR's (SP III and SP 2650), I still don't have the basemap - CN issue fully figured out. Maybe 99%, but not fully - I still get surprises.
What I have noted that is of interest to us as moto riders is as follows: The basemap doesn't do much for us in urban areas that are well covered by CN. It does become very important in rural areas that are not well covered by CN. I don't know what CN coverage is like in the British Isles (having only spent one summer riding there), but I am pretty familiar with the basemap - CN issues in Canada, the USA, and Western Europe.
In Canada - for example, northern Ontario or anywhere in Alberta - the basemap will have a whole whack more roads on it than CN will. Problem is, we don't see any of these roads on the basemap unless we turn off the CN map segments for the area we are in, because the CN map segments will always "overlay" and hide the basemap, even if the CN segments have less data in them.
I have often tried to generate a route from A to B in rural Canada or rural USA, and had the GPSR (running the most up to date version of CN) fail to generate an appropriate route. It took me some time to realize that if I turned off the CN segments, and allowed the basemap to do the route generation, I would then get a pretty good route.
The cause of this problem is that NavTech has not yet mapped the whole darn world. I don't know how long it will take until they get it all done - probably a few more years - but until then, the basemap is a very good "out" when working in areas that have spotty coverage by CN. As of the end of last summer (last time I did a lot of riding), rural Western Canada (Manitoba, Saskatchewan, Alberta) had pretty spotty coverage on CN, and rural north-western USA (Idaho, Montana, etc.) also had pretty spotty coverage. The Canada MetroGuide 4 that was released at the end of 2003 has probably addressed the holes in the Canadian coverage - and it supports autorouting. So, if a user has CN and MG Canada 4 loaded, all he or she has to remember to do is to turn off the CN segments once out in the rural areas, to allow the MG Canada 4 segments to take over.
In the USA - I don't think they really have a good fix for this yet. I have heard that MG USA is based on slightly different cartography than CN NA, but they both come from NavTech. I think the basemap will be pretty essential for rural riding in the USA for some time to come. I encountered a number of problems where the CN data was missing a "connection" between roads - in other words, it looked like a route should have been possible, but the GPSR would not generate a sensible route with CN - where the only "out" for me was to switch off CN and use the basemap, which did not have the same digitization error.
In Europe, I have observed that CN coverage is close to perfect in Benelux, Germany, and Switzerland. It becomes spotty in the Republic of Ireland and in the romance language countries. Again, the basemap is much better than CN when outside of urban areas in these countries. The basemap will support autoroute generation in areas where CN won't, provided you turn off CN first, to allow the basemap to take over.
Although I suspect that WorldMap probably has about the same level of detail as the basemap (meaning, probably the same number of roads, highways, etc. per 1,000 square km's), WorldMap is a bit older than the autorouting basemaps (American or European), and WorldMap won't support autoroute generation. A good example of this is in Spain, where many of the recently constructed major motorways (multi-lane toll roads) were missing from the previous edition (last year's edition) of CN, but they were there on the basemap. They were missing from WorldMap, because WorldMap was published long before these roads were constructed.
Best way to test all this out on your own (it will make more sense to you once you see it displayed on your own GPSR) is to go out to a remote rural area, zoom out to a scale that shows the secondary and tertiary roads (but not the streets), then look at the CN picture. Now turn off the CN mapset and look at the (remaining) basemap picture. Often roads will appear from the basemap detail where there were no roads in the CN detail. If you also have WorldMap loaded, you can then compare all three - CN, WorldMap, and the basemap - by switching mapsets on and off.
I don't know what the quality of the current CN coverage in the UK is - if, for example, it is as complete and comprehensive as it is here in Switzerland, then who cares, you don't need a basemap at all. But, if there are any holes in it (meaning, if NavTech does not have 100% remote rural coverage of the UK), then the basemap is a very useful tool to have.
In another 3 to 5 years (when NavTech gets everywhere covered, 100%), all this won't matter. But at present, it does matter to riders who are doing long-distance trips. For folks who are just driving around in the same big city all the time, I suppose it hardly matters at all.
Just a final comment - you mentioned your eTrex - I don't know much about those, but be aware that there are two different basemaps for each geographic area, one which supports autorouting (SP III, SP 2650), and one that does not support autorouting (other ones). I doubt if the data is the same in each of them, simply because the auto-routing products came along later.
Hope this explains it better.
PanEuropean
). I travel in France a lot and it's a different story there altogether. I wish I had known about how the base map works in relation to CN etc as you described, and in your previous posts as it would have saved me a lot of ( shall we say frustrating moments
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