Strava's GAP Feature

There is a really cool feature on Strava called GAP.  

Grade Adjusted Pace estimates an equivalent pace when running on flat land. Because running up hill requires extra effort, the Grade Adjusted Pace will be faster than the actual pace you ran. When running down hill, the Grade Adjusted Pace will be slower than the actual pace. The steeper the grade, the larger the adjustment. Now you can see the effort and compare hilly and flat runs more easily. The calculation of Grade Adjusted Pace was inspired by work done by C.T.M. Davies studying environmental effects on running.

Since all my running  has hills, this is really interesting to me.  Below is a 13 mile training run I did earlier this year.  The elevation chart looks like this:

Lots and lots of hills!  I'm not completely convinced with some of the adjustments.  Mile 5 had 170 feet of climbing, so an adjusted pace of 8:11 from 10:37 might be right.  I don't understand how mile 7 with a loss of 79 feet adjusted downward, although there was some climbing at the beginning of that mile.  Mile 8 had 188 feet of climbing, but I've never run a 6:32 mile, so again I have some doubts!

	Elevation	GAP	Actual Pace
Mile 1	78 ft	9:05	10:36
Mile 2	-68 ft	10:56	11:11
Mile 3	65 ft	8:43	10:07
Mile 4	-90 ft	9:51	9:39
Mile 5	170 ft	8:11	10:37
Mile 6	20 ft	9:07	11:04
Mile 7	-79 ft	8:12	10:19
Mile 8	188 ft	6:32	12:03
Mile 9	-104 ft	8:41	10:29
Mile 10	-160 ft	9:27	9:11
Mile 11	42 ft	11:16	13:25
Mile 12	40 ft	11:19	13:47
Mile 13	-78 ft	12:09	13:01
0.56 mi	-24 ft	10:42	11:46

I guess I just find this very interesting since I do so many hills on any given run!  It might also explain why I'm so tired at the end of 15 or 20 miles.