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Best accuracy: Google Maps or OSM

Former Member over 8 years ago

today I started planning a route starting at the Aguile du Midi station, following the arête down then around to La Vallee Blanche I started out using OSM aerial imagery, plotted a track along the route which all looked good, then for some reason I switched the view over to Google Maps and noticed that the track I had plotted was no longer on top of the path visible in the image, its hard to estimate how much it was off, but I would guess in the region of 50-100 metres... enough to land you in trouble if you were to blindly follow the GPS track!

This got me thinking which one of the two images is most accurate? Anyone here have any thoughts? has this been noticed before?

0 billhart46 over 8 years ago

In my area I have not noticed that any offset between the different maps. But I have notice that they differen in small roads being missing off one and others missing off of the other map.

0 Dr Phil over 8 years ago

I would never blindly follow any route that I've created online with any mapping service, especially trails. Roads are generally ok though. If I am following a trail and it appears to deviate away from the plotted path, I'll keep on it as long as it is still going in the general direction. I use a 920 and quite often the plotted track I am following will be 10s of metres away from my plotted path. But I generally reconnect in the end.

This point, BTW, is often overlooked when people whine about GPS accuracy. Just because the resultant line Garmin draws is off trail does not mean that the device is any less accurate. Trying to place a 2D line on a 3D surface is not easy.

0 Former Member over 8 years ago

I would never blindly follow any route that I've created online with any mapping service, especially trails. Roads are generally ok though. If I am following a trail and it appears to deviate away from the plotted path, I'll keep on it as long as it is still going in the general direction. I use a 920 and quite often the plotted track I am following will be 10s of metres away from my plotted path. But I generally reconnect in the end.

This point, BTW, is often overlooked when people whine about GPS accuracy. Just because the resultant line Garmin draws is off trail does not mean that the device is any less accurate. Trying to place a 2D line on a 3D surface is not easy.

You are right there, sure I would never blindly follow any route created using image data from any photographic mapping service. I guess it comes down to the view angle from which the photograph was taken, as well as any distortion applied when the images are stitched together.

I was at work when i was working on this route and only had access to the mapping options provided by garmin connect, At home I use Memory maps or Basecamp to create routes as these are based around real topographic map data & many times I have compared the planned route with the GPX track from my GPSMAP 64s and found them to only differ by a few metres. even with this level of accuracy I would never blindly follow the route, a certain amount of common sense has to come in to it, but if a route is off by a considerable amount it could make navigating with it very tricky.