The Octopus 

I've heard it explained -- and it seems to make sense -- that GPS measurements will run low in rolling terrain because they're only taking measurements every so often, which results in the ride effectively being "flattened out" -- the peaks and valleys get rounded off, if you will. On the other hand, the numbers that TOPO USA gives seem to be silly high. But my understanding of that software is that it's counting every miniscule change, however small. Those can really add up. Around here, TOPO USA and my GPS (Garmin 60CSx) differ wildly on the climbing on any particular route. Error rate is about 30% -- TOPO USA being 30% higher than the GPS, that is.

Interestingly, both TOPO USA and the GPS agree on any given, sustained pitch. For example, Jack Run -- one of the nastiest, longest climbs in the state -- measures the same, bottom-to-top (a little more than 400 feet), on both. When I rode out in Mt. Rainier National Park this past summer, both also agreed on the bottom-to-top elevation change of the one big climb (as in 3.6K feet big) that I did out there. The differences seem to be in rolling terrain.

Rollers do add up in a big way, and they also really affect people very differently -- I think differently than the longer, sustained stuff. How x-amount of climbing feels in rolling terrain will depend a lot on the strength of the rider. Fast or strong folks can rock and roll in the rolling (punny!) terrain, carrying speed on the down-hill and pushing an aggressive gear over the top of the next rise, maintaining a lot of momentum. Rinse and repeat. Less fast riders might not be able to push the big ring as aggressively down the slope and might end up gearing all the way down to granny to clear the upcoming rise that the faster/stronger rider cleared without ever leaving the big ring. In this neck of the woods, riders who can effectively sustain repeated bursts of high energy are the most effective "climbers." Out West, where the "climb" is a 4-6% grade for 20 or more miles, the strong climbers are folks who can put out the highest constant wattage over a long period of time. These are very different skills, and someone who is good at one might not be so good at the other. So, anyway, by whatever decive measured, x-feet of climbing isn't the same in different places in the country. The 7,000 feet of climbing on our 200K means you're riding rolling terrain for 200K. But 7,000 of climbing in some parts of the country means you've got to climb two passes and then ride along a dead-flat river valley for 120K.