Last Wednesday we went down to Penn's Landing to hang out with a bunch of people staring up at a big balloon.

The Philly Tech Week event was meant to teach the geographically inclined how to map things on the cheap.

If you're, say, a group of fishermen concerned about the impacts of the BP oil spill, you probably can't afford your own satellite. Balloon mapping provides an affordable alternative — and has drawn plenty of interest from geographers, technologists and journalists alike.

Almost two-dozen folks showed up to the balloon-mapping workshop last week. Two balloons captured over 600 images from hundreds of feet in the air.

Above are the initial fruits of that labor: Some of those images stitched together and plotted onto an interactive map.

The Public Laboratory for Open Technology and Science offers a full-screen experience.

Or you can visit Flickr for some of the raw images.