GPS Accuracy - Garmin vs Smartphone...

The first thing to look at is how often each checks the satelight.  If your phone does it every 5 seconds, and the garmin every one then it is more likely not to miss some detail.

But it might be a matter of where you are carrying them, and how the route goes.

For example, if one is on your left wrist, and the other is in your right pocket, the one in the pocket might get fewer updates.  But it might happen that the wrist misses the last few feet before a turn around while the one on the right just misses that the trail veered left and back to the right.

With that big of a difference I would use map my run, gmaps, or the route section here on BT to check the distance.

The streets I live and run around on are a grid, so when I go for a run the distance from street intersection to street intersection is always either one mile or half a mile. My Garmin 305 is always spot on for the distance and I see no noticeable variation in distance measuring, so my vote is Garmin.

If you really want to know I'd suggest running a known distance and seeing which device comes the closest to what it should be.

I wonder how often any GPS unit "drops points."  I use a GPS at work for measuring fields and if I select "route" it drops a point depending what you set it for, 5 seconds, 7 seconds, etc.  If I turn a corner, I pause to make sure it drops a point or two at the corner. 

My running partner uses RunKeeper on his iPhone & we run several laps on a 1 mile route through town.  His maps look like he walks through peoples yards, cut corners & w/ today's through some houses.  We stay on the road, but that is what the map looks like. 

I don't have a Garmin or anything similar so I don't know if you can set the device to drop points more often.  Granted, with dropping more points, that is more data & memory. 

FWIW, in all likelihood, that demonstrates some (very) modest inaccuracy.  On a standard (400m) track, you have to go a little more than 4 laps for 1 mile (on the inner lane).  Which means the point on the track where you 'click' a mile should change as you run more miles.  If you are on an older track that is 440 yards, then your Garmin is coming up more accurate.  (Of course, you shouldn't need a Garmin to tell you how far you have gone on a track anyway.  )

I'll urge you to go check out DCRainmaker's blog (just google search the name, it'll be the first hit).  He has done MANY tests with upwards of 10 GPS devises on a distance measuring wheel.  The accuracy is very dependant on speed, course, and line of sight with the sky.

I'll urge you to go check out DCRainmaker's blog (just google search the name, it'll be the first hit).  He has done MANY tests with upwards of 10 GPS devises on a distance measuring wheel.  The accuracy is very dependant on speed, course, and line of sight with the sky.

I would say the garmin. I have used runkeeper on my iPhone and I now have a garmin 305. The garmin definitely  samples more, so as others have mentioned, the iphone cuts corners more.

 My iPhone would sometimes throw a point a couple hundred feet off the path and artificially bump up the distance but this seems to have improved with software updates.

One advantage to the smartphone is it can find the gps signal quicker by using the cell phone towers to get close before 'looking' for the satellites.

I know that on my Garmin 205 I discovered online a couple years ago that it has two settings for how often it takes a distance/pace reading. The default, I believe, was every 5 seconds. I had to manually choose every 1 second. I read something about it stores less data that way, but I haven't run into any problems yet. I guess I don't run enough. 

In regards to a cell phone tracking a run, do you guys know if the running APPs use the cell phone base transceiver stations (likely) or satellites? I can't imagine a phone being tracking that minutely. Unless Steve Jobs is after you.

Garmin antennas are made (shape, sensitivity, density) specifically for accuracy.  Phone GPS antennas are made specifically to fit into a phones form factor.  Phone GPS is to get general GPS, but it is less likely to be within 2.5meters that Garmin specifies when you are moving the antenna around.

Garmin is more accurate based on the antenna shape and sensitivity.

I have a friend who has endomondo and he says it sucks and he's ditched it for a garmin.  Look at this log and you'll see why:  notice how not once do his laps actually repeat each other, nor are they ever truly on the trail...but that 54mph sure looks sweet!

http://www.endomondo.com/workouts/vXiuXJCfiEg

To clear a few myths: 

1)  GPS is not line of sight.  It is RF which can travel through many different materials.  Dense material such as concrete and rock will inhibit signal (In cities or deep valleys), however lighter material such as wood should not greatly decrease the signal quality

2) GPS units talk to satellites 1000's of times a second and are constantly calculating the time deltas.  GPS Chipsets can be configured to "Output" the results at different intervals (1 second, 5 seconds,etc).  Better GPS chipsets can output position data 10 times a second. http://www.sparkfun.com/products/8975

nice tests! Thanks for posting the results.

I've been trying to decide if I should move from my iphone 4 and runkeeper to a garmin watch.

I do disable the wifi anytime I use runkeeper, hopefully that helps, especially on your walking results, but riding and running look pretty good.