In my offline life, I am a graduate student in geology-- specifically, I study how gravel, sand and mud are transported by rivers and the oceans, and the patterns they make as they are buried (or not!) by more sand and mud and gravel.
Some of the largest deposits of this kind of stuff are river deltas, and another graduate student and I have developed a crowdsourced game where the users classify deltas by shape. It's deliberately very freeform: we give you 5 to 13 images of river deltas and you simply drag and drop images that you believe look similar into groups. (Or, if you don't think a delta looks similar to any other, don't group them. That's also really useful information.) The criteria you use for similarity are up to you-- we're trying to develop a classification system* from your responses. There are no wrong answers. At all. We'd love it if you added tags to the groups to let us know why you grouped them together, but it's not a requirement.
If you're interested (or simply have five minutes to kill), please check it out at
deltashuffle.umn.edu*Honesty compels me to add that there is an existing classification system, but it runs on interpretive thinking-- "This delta is type R because it looks like a type R delta" rather than observation alone. And everyone who is professionally interested in this sort of thing has already been brainwashed into the system to the point of being unable to see deltas in any other terms.
