GPS Map Accuracy

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The Tests ... cont/d

While surfing the GPS websites, I found GPSnuts (www.GPSnuts.com) and noticed they had a Canadian section. There I found a review of the Garmin Mapsource Canada maps, and noted the reviewer had found similar inaccuracies with the maps.  What was interesting was that he'd used CDAL points to verify road intersection locations.  I'd never heard of CDAL but it didn't take Google (www.google.com) long to track it down to a Canadian Government office in Quebec.  The bad news was that they had closed their database to the public so I thought I was at a deadend.  The good news was that I then tracked down the guy that did the GPSnuts review (would you believe he lives quite near me and is a sponsor of the Kawasaki GPS Trail Ride series!) and he shared his CDAL database points with me.

It was interesting finding out how to get these points in the MapSource and MapSend maps (that's for another report), but once in there it was amazingly easy to check the map accuracy at almost any point in Canada.  Here's a few examples of typical areas I ride my Dual Sport motorcycle - the Oakville/Milton area, Orangeville, Coe Hill near Bancroft, and the 5 Points area near Bobcaygeon.  To interpret these maps, look at the scale and then notice how far a CDAL point (6 digit waypoints) are from the intersection of either roads or railtracks.
 
 

This is a screen shot of an area just north of Burlington using the MG map.  You can see the CDAL reference points (6 digit waypoints 078xxx) are coincident with the actual road intersections.  This would appear to be an accurate section of the map.
Switching to the EBM, this is the same area as above, showing the same CDAL points. 
The location of the points varies from very close to about 200m from the actual intersection.
The Magellan MS map demonstrates excellent accuracy, and is very detailed on natural objects (streams, lakes, etc) but fails to show railway tracks, which are useful for dual sport rides, especially if abandoned!

 
Unfortunately, the MG map accuracy varies within a small area. 
This shows the region NE of Orangeville on the MG map. 
The black road is Hockley Valley Rd, and the CDAL points are about 300m from the road, but on Hwy 9, just 2-3 Km away, the points are perfectly aligned. 
This EBM image of Hockley Valley Rd is a closeup of part of the area above.
It shows errors of about 300m on all the intersections. 
Pity, this is one of my favourite riding areas!
This is the same area as above, but is shown on the Magellan MapSend (MS) map.  The detail is much superior to the Garmin maps PLUS the CDAL points are perfectly aligned with the intersections. 
If only Garmin maps were this good!  A Canadian Government 1:50,000 Toporama map of the Orangeville area.  Need I comment on the accuracy?

My observations are:

  • The MetroGuide maps are very reliable in urban areas and for major roads.
  • The Enhanced Base Map varies from 500m errors to zero error, depending on the region.
  • The Canadian Government topo maps are spot on.  BUT, and I'm guessing here,  this may be because they are the source of the CDAL data.
  • MapSend Streets & Destinations Canada map has superb accuracy in the areas I checked it, and much more detail than Mapsource maps.
  • The downside to the extra detail of the MapSend map is the amount of memory required to load enough sections for a reasonable trip.

Conclusions

My overall conclusion is that the EBM is not suitable for Dual Sport motorcycle route planning, but would be fine for finding your position if you were lost.  The MapSend maps would be my choice.  Unfortunately, the choice of maps is not usually relevent if you already own a GPS.  In my case, I selected the Garmin eTrex based on user experience and without knowing the relative merits of each brand of mapping software.  The Garmin maps will suffice for approximate position checks on the GPS screen, but I doubt they will be usable for detailed routes I need to create on my PC..

For planning organized rides, where it may not always be possible to pre-ride the route, I expect to only use Topo maps.  SoftMap Topo50, with the GPS plug-in, seems the easiest to use at this stage.  I haven't used OziExplorer enough to know if there are any shortcuts, but I find it frustrating that it only handles one small map at a time, whereas, SoftMap has all of Ontario in a seemless single map (almost, apart from the White Hole near Bancroft!).
 
 

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