What is under your feet?
Crust thickness is a start at story telling. I'd love to be able to say "You're where? In Boston? Ok, you are standing on glacial till (link), atop mumble from mumble, and mumble (n km), and Grenville basement (link)". But... I've not seen such data. So... small steps.
Can you find... somewhere with 10km of sediment? Two places with crust thicker than 60 km? What else?
... Mark it up!
The CRUST2.0 dataset provides crustal thickness on a 2° global grid.
The CRUST2.0 elevation data is from ETOP05.
A new CRUST1.0 (1° grid) is in development.(2011-2012)
Earth image: NASA Visble Earth
Doables: A transect line should be drawn on map and globe. Mention cross-section scale/length (1 Mm). Unintended white lines on cross-section - bug or feature? When the globe is upside-down... how confusing is everything? Mousing the cross-section could control display. Mousing the key could highlight cross-section layers (to better see thin layers). The cross-section could be zoomable. The cross-section could be interactively specified (click-drag drawn on the map). Tweak colors to improve distinguishability (water vs crust, ice vs background). Gracefully handle moving along map edge. Make globe surrounding non-selectable. Is globe rotation and control discoverable? Test on tablet.
Doables: The demo code could be isolated, to encourage contribution, adoption, and takeover. And componentized for mashups.