I don't think there would be any need to send a balloon. Unless they were after some non-obvious data. Aerial images and topography data can be gotten online. In many cases you can download this data for offline use. While online activity can be tracked, I think getting the data online would attract less attention than flying a balloon around the world.

To sample what sorts of data is available, try the Organic Maps app. I recommend everyone get it. It's totally free and open source. Everything works offline, even navigation.