Map accuracy in the Whites.

[Neil]

How accurately are the trails depicted on the maps that come with the AMC White Mtn. Guide?

How accurately are they depicted on the USGS Quads?

I'm primarily interested in the Bonds, South Twin, Garfield, Franconia Ridge, and the Osseo Trail.

 

[ColdRiverRun]

You could just ask if anyone has a track log of that area.. or did you?

 

[bryan]

i think the current amc maps are probably pretty accurate as to trail location. the osseo trail and lower bondcliff trail are the only places i can think there might be discrepancies depending on the age of your maps. an older usgs quad might show them in different places. i know some mapping programs i have do.
have fun if you end up attempting the pemi.

bryan

 

[Bob Kittredge]

I seem to remember hearing that the latest AMC maps show the true (according to GPS) locations of the trails, but the topo maps themselves are based on the USGS quads which do not place features like summits and streams quite so accurately. This can cause confusion when stream crossings don't come where you might expect them from looking at the map.

Can anyone verify this? Or is it just something I dreamed while I was napping with my cat?

 

[Neil]

have fun if you end up attempting the pemi.

What tipped you off?

 

[DougPaul]

There are formal standards for the accuracy of USGS Topos: http://rockyweb.cr.usgs.gov/nmpstds/nmas647.html

1. Horizontal accuracy. For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale; for maps on publication scales of 1:20,000 or smaller, 1/50 inch. These limits of accuracy shall apply in all cases to positions of well-defined points only.
2. Vertical accuracy, as applied to contour maps on all publication scales, shall be such that not more than 10 percent of the elevations tested shall be in error more than one-half the contour interval.

1/50 of an inch on the map comes out to 12 meters on a 24K scale map and 51 meters on a 100K scale map.

A consumer GPS is generally accurate to within 10 meters (error less than 10 meters 90% of the time) in good signal conditions. Professional mapping GPSes can be accurate to the several millimeter level.

The AMC White Mtn (95K scale) maps appear to be based upon 100K USGS topos. Thus the representation of trails on these maps is probably limited by the accuracy of the maps rather than the accuracy of the GPS tracks of the trails.

Doug

 

[nartreb]

The AMC maps are updated frequently (with each new edition of the book, so every few years), whereas the USGS maps are not. The most glaring example of this is the Osseo Trail: the USGS maps show the old route from the Kanc (now in the parking lot of a condo complex) over Whaleback; the AMC maps show the "new" (ten years old? Twenty?) route that starts from the Lincoln Woods trail [right at the point where the name changes to Wilderness trail] and climbs Flume from the East. (This is mentioned in a FAQ I'm sure you've read somewhere...)
The AMC maps are on a scale that doesn't show enough fine detail to be very useful for bushwhacking, but are fine if you stay on the trails (which are pretty easy to follow). Some micro-scale relocations around streams or landslides (I seem to recall a couple on Bondcliff trail) are too small to show up on the AMC map, but they're too small to worry about anyway: in the unlikely event you take a wrong turn, you'll be back on the official trail in a couple of minutes.

 

[sardog1]

After several experiences of my own and others with the AMC maps, I have tucked a reminder in my cerebral cortex: "The map is to be suspected when approaching crossings." Otherwise I have found them to be generally pretty good.

When I teach navigation, I tell people that they're ready to solo in the backcountry when they start noticing map errors.

 

[Neil]

The AMC maps are updated frequently (with each new edition of the book)

I have the 27th edition.

I noticed the Osseo trail discrepancy, I'd be in big trouble I guess if I didn't .

(The USGS quads for the Adirondacks are not to be counted on when it comes to man-made features and even with respect to some swamps - those darned beavers!)

Your Pemi Loop page is excellent btw.

 

[Paradox]

This might be about as accurate as you can get or need.

http://www.wikiloc.com/wikiloc/view.do?id=323622

 

[Neil]

This might be about as accurate as you can get or need.

http://www.wikiloc.com/wikiloc/view.do?id=323622

Maybe but the source seems pretty dubious.

 

[Paradox]

Add this to help you tag Zealand
http://www.wikiloc.com/wikiloc/view.do?id=705464

Add this to help you tag Galehead and North Twin:
http://www.wikiloc.com/wikiloc/view.do?id=726988
This latter one is as dubious as it gets.

 

[ferrisjrf]

...the source seems pretty dubious.

Don't trust that track. I heard that guy's a loser.

Actually, I think it's pretty much right on, except between Guyot and South Twin, it may have strayed a little bit.

 

[Kevin Rooney]

Neil -

As I recall - several years ago Larry Garland used a GPS and hiked the trails, which were then used in the production of the AMC WMNF maps. Aside for minor re-routes, there have been few changes since.

As noted above, non-trail features may be somewhat mis-located. Streams are tough to define accurately, as flooding can cause a channel to be relocated.

 

[Neil]

It looks as though my maps (AMC 2xth edition and Topo! (USGS Quads) line up pretty closely and also match Jason's Wikiloc thingy. (just wondering, if you download from there is it a .gpx file?)

I doubt I'll be carrying a gps because I'm a Luddite. Much more fun to depend on my formidable raw brain power (and Mastergrasshopper's phenomenal visual memory) than satellites. Hopefully no snowshoes either. (We'll all be wearing buckskin, too.)

 

[Dr. Dasypodidae]

Neil -

As I recall - several years ago Larry Garland used a GPS and hiked the trails, which were then used in the production of the AMC WMNF maps. Aside for minor re-routes, there have been few changes since.

As noted above, non-trail features may be somewhat mis-located. Streams are tough to define accurately, as flooding can cause a channel to be relocated.

Yes, Larry and his crew, one of whom was a former student of mine, used a Trimble GPS surveying system (x-y accuracy sub-meter; z not so good, but still more than good enough for the 50- and 100-ft contour interval used on the AMC maps) to locate all of the trailheads and trail junctions in the mid-1990s, which have been carried over to all latter edition maps. But, I would still not believe the 4025 ft elevation for whichever summit of Owls Head is shown.

 

[drewski]

OR--as rik says..you could just stay in the daks...

 

[DougPaul]

As noted above, non-trail features may be somewhat mis-located. Streams are tough to define accurately, as flooding can cause a channel to be relocated.

I believe much (most?) of the original mapping was done from aerial photographs plus some on-the-ground surveying. Small streams, trails, etc can be hard to locate under the trees.

Some more modern mapping has been done by airborne/satellite radar which has a better chance of seeing through the trees. Don't know how well trails and small streams will show up. (Stream gullies should show, just don't know about a small stream on relatively flat ground.)

Doug

 

[psmart]

As others have noted, discrepancies in stream locations are the most common map errors you're likely to come across in the whites. In some cases a notable stream may not appear on the map at all, or a trail may appear on the wrong side of a stream. The latter is very difficult for a modern cartographer to correct: Their only choices are re-mapping the stream (which would take much more time than mapping the trail itself) or fudging the GPS data for the trail, so as to show the correct relation to the stream. So these discrepancies are likely to continue to exist.

 

[Paradox]

It looks as though my maps (AMC 2xth edition and Topo! (USGS Quads) line up pretty closely and also match Jason's Wikiloc thingy. (just wondering, if you download from there is it a .gpx file?)
.)

Yes, easy to manipulate in mapsource.