[pct-l] Data Book Discrepancies

[Gail Van Velzer]

Dan aka Thumper,
Thanks for clarifying in a very nice way.  I will bet Halfmile's data is 
closer only because the GPS data is new and more accurate.  The USFS maps; 
some of them dating many years back, were made by survey methods, which was 
the most accurate at the time, but I have seen the USFS, or USGS maps off. 
If you start with a faulty point, everything else will be faulty after that. 
The current GPS waypoints are accurate within a few feet, whereas survey 
methods can vary depending on the surveyor.
Gail aka Golly

----- Original Message ----- 
From: "Dan C. aka Thumper" <dofdear at cox.net>
To: <pct-l at backcountry.net>
Sent: Wednesday, June 11, 2014 9:54 AM
Subject: [pct-l] Data Book Discrepancies


> While I'm not surprised this conversation has become personal it is 
> disappointing. Particularly from a successful hiker who really appreciates 
> the data.
>
> What is clear to me is that both Halfmile's and Postholer's data is 
> 'correct' and accurate. So how can they both be correct and different at 
> the same time. Well that's easy. The source infomation and technical 
> processes are different.
>
> Halfmile uses GPS tracks he and others collected, and then put them 
> through rigorous processes to produce his maps.  His process is as 
> accurate as the GPS equipment and hikers used. I find it interesting that 
> Halfmile is currently hiking with a professional surveyor type accurate 
> GPS in an effort to increase confidence levels.
>
> In Postholer's case he is using officially published data sources 
> including the USFS kmz files and other geospatial data sources. He employs 
> recognized processes to calculate distances and elevation.
>
> Personally I find both map sets have benefits with Postholer's easier to 
> read in the field plus the accompanying data book. But Halfmile's map 
> tracks may in a few cases be closer to the actual trail. But 10 miles in 
> some ~2680 miles is pretty close.
>
> I know both of these hikers. They have character and most importantly, 
> integrity. They both respect and obsess over data. Either map set will 
> work well.
>
> Interesting is that of late Google Maps displays a trail track of the PCT 
> and many other trails.  Wonder what their source was? Bet not Halfmile 
> (just my opinion). Suspect they are using an authoritative source, 
> although if they are documenting trails like they did roads I'll be 
> applying for work as a Google Hiker.
>
> Finally, it is not the PCTA's charter or responsibility to adopt a 
> standard. For that we should look to the USFS, BLM and the other maping 
> agencies.
>
> Thumper
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