I'm a UX product designer who specializes in data visualization, interactive media, and multimodal interaction. Former UX engineer who loves to prototype in code.
I see a handful of parallels between Tumblr, Twitter, and Instagram--aside from the ability to re-post, of course--so I'm surprised how little work Instagram has put into content discovery.
Aside from the initial load Instagram's explore feature, its difficult to see what images are trending, and hard to organically search photos tagged at a given location unless you navigate to a photo tagged with that given location first.
Traffic management is a fascinating intersection of sociology, fluid dynamics, behavior change, and urban planning.
If you're interested in this field, I can't recommend the work of Tom Vanderbilt enough. His book "Traffic" brought urban planning to the masses in the same manner "Freakonomics" made social and public policy accessible.
This reminds me of a similar exercise to find the optimal viewing order of Battlestar Galactica episodes, movies, web-series, deleted scenes, extended episodes, etc.