I'm currently planning a 5-night trip through Kings Canyon in a couple of weeks, and I'm finding a lot of differences in trail mileage estimates among various sources. For example, some of the trail mileages I've found from Road's End to the Woods Creek Crossing (JMT) are:

Nat Geo Map - 13.5
RJ Secor - 15
Falcon Guide and other trail books - 16
nps.gov web site - 17

That's around a 25% difference from lowest to highest. Not a big deal for a 1 or 2 day trip, but could be significant over a 75-mile trek. May even require planning for an extra day. There are many other examples out there as well.

So who do you trust? Nat Geo? NPS? Or just add 'em all up and take an average?

I trust the first one.

I certainly wouldn't go by nps.gov!

We hiked the High Sierra Trail from Crescent Meadow last month and went over Colby Pass to Lodgepole (94 miles total RT). There were huge differences in posted mileage between Sequoia and Kings Canyon. Up to 20 percent longer on several segments. We normally make our own measurements off of a topo map but in the field or in the various guides, we find totally messed up mileage postings.

We just bring half a day of food extra and live with it. If we absorb the extra miles each day, no big deal. If it slows us down, we stay extra day. Either way, it should not be a big deal unless you hike over great distance, something over 100 miles or so, or you must be in the office tomorrow at 9 am with 25 miles to go. That could be a bummer.... You could try to average the miles, with the result being either a pleasant surprise each day or not...

Natgeo tends to be a little short, especially if there are switchbacks. Check the Tom Harrison Map for that area, they are usually very accurate. My guess is 15.375.

I've found the Tom Harrison maps to be more accurate than most others. I never do a Sierra trip without one.

I'd go with the National Geographic maps. In my experience, they are the best overall. The Tom Harrison maps are nice but are not as detailed as the NG maps (typically wider contour intervals). That's why I left my TH map behind at Onion Valley the other day and kept the NG one that covered the same terrain.

Don't trust NPS and FS signs. Many are based on old measurements by outdated methods. Last summer in Montana, I found a sign-to-reality difference of 9 to 7 miles. That's significant on a day hike, but apply that to a long-distance haul and you are talking about major differences!

hillmap.com is your friend. use the path tab

Thanks all, will pick up a TH map this weekend.

ps. that hillmap.com site is pretty cool too!

None of the sources can be trusted when the trail drawn on a topographic map is incorrect. All depend on the USGS topo trail markings being correct except when someone has corrected a map which is rare. For example in this thread I used the satellite image to correct the Shepherd Pass trail and found the actual trail was quite a bit longer:

post910163.html?hilit=shepherd#p910163

Bob Burd overlayed his GPS track that matched closely. There are actually quite a number of trails with bogus trail markings especially in forested areas where a satellite image is useless and the actual trail on the topo is merely a guess. However now with GPS tracking we can reasonably accurately show where trails actually route. However there is no community of users posting corrections to trails. A couple weeks ago I backpacked from Mineral King over Sawtooth Pass. The trail between Groundhog Meadow and Monarch Lake to the Crystal Lake junction is one of the worst drawn. Would appreciated if someone on this board would post a GPS track. Aligning such tracks to a topo takes some more advanced Photoshop skills, some of which I related in the above thread.

Programs like ExpertGPS will plot your tracks on the USGS topos. You can then save screen dumps.