This map is getting quite some attention on Twitter, I don't know who made it, but I thought it would spark some interesting discussion here.
BdvlhlmCAAA2YER.jpg 101.59KB 28 downloads
So it appears every uphill street is shown as a slope diagram. It's a sort of birds-eye view anyway so the distortion that that approach brings is irrelevant. I'm not sure about the color scheme though, most of the ones I've seen (in the cycling community) use a green-yellow-red progression, although blue and black are sometimes used as well.
They're not kidding about the "very steep street" by the way, for kicks I checked Ballarat Street on Street View. Seems to be about 15 degrees slope, that's 30%...