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Discrepancies between Google and postholer versions of AT

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Discrepancies between Google and postholer versions of AT

Postby pfletch101 » Mon Sep 03, 2012 7:01 am

The 'generic' version of Google maps shows the AT for much, but not all, of the southern part of its course - I have been mapping and (virtually!) walking it from the southern end on Ifit Live. In addition to a few sections where (on the 'generic' map) the trail just disappears, to reappear a few miles further on, there are a number of places where the map here shows more detail (e.g. zig-zags which are not shown on the 'generic' version). This is not terribly surprising, and speaks to the work that went into the map here. However, I have recently run into a section, north of Roan Mountain in northern Tennessee, where, after disappearing, the trail reappears on the generic map with a slightly (but significantly) different course to that shown here, eventually rejoining the course shown here a few miles further on. I saw elsewhere that your map data is a few years old, but I did not think that the course of the trail changed significantly from year to year. Which version is likely to be correct, on the (current) ground?
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Re: Discrepancies between Google and postholer versions of A

Postby postholer » Mon Sep 03, 2012 9:19 am

First, thanks for the kind words on the postholer maps!

I would not rely on the 'generic' trail trace for any trail on google maps, nor Delorme maps, nor NatGeo Topo maps as they are all wildly wrong. While I can't speak for any other custom google map traces out there on the web, the postholer maps use the data from the Appalachian Trail Conservancy, which was last updated in 2009.

There is a big difference the way the trace is rendered on postholer maps compared to other custom google maps as well. I've seen most other AT, PCT trails and can say with certainty that they all lack detail at any zoom level. The postholer maps do not suffer from those issues.

Now, is that to say the postholer trace is exactly perfect? Of course not. Given my experience with this sort of stuff I would say that you'll find a number of variations, most of which are small. Again, I rely on the ATC trace, so that is what is displayed.

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Re: Discrepancies between Google and postholer versions of A

Postby pfletch101 » Thu Sep 06, 2012 6:31 am

Thanks for your very prompt reply. I thought that the maps here were likely to be more reliable. The problem is that, if there is no marked trail on the Ifit/Google map, I have to transfer the track, point by point, by eye between the postholer map and the Ifit/generic Google map (with both in satellite view to give context). If there is a marked trail, the Ifit software allows you to follow it. While the manual process can be done, it takes a lot of time. Ifit doesn't (yet) support the uploading of tracks in GML format. I think that I am going to have to use the marked version for my virtual workout, where it exists, and only fill in the gaps by hand, but recognize that I am, to some extent, "cheating".
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