Gee, I'm not sure. I guess it's hilly if I stand up on a lot of hills? My ride last Sunday was hilly. One huge hill (series of steep climbs - not a mountain, but it has "mountain" in its name - from the opposite direction it is right at my limit), one very big hill, one major grinder, and lots and lots of rollers and lesser grinders. We don't have mountains, but we do have what I consider to be big hills. It is possible to find flat routes, but generally, if I ride from home or for much distance, I will hit at least one big climb. If you plan it carefully, you can map out a 50 mile route that will hit 5 significant climbs. I haven't found anything around here that I can't ride with my standard double, but a couple are touch & go, standing up and giving it everything I have. Twice last year (on the afore-mentioned hill, coming up the steep side) I had what felt like split-second wooziness - like all the blood suddenly flowed out of my brain, but then I was okay.

I didn't do the survey - I haven't ever measured the elevation changes on my rides.