The airwaves can be a cacophonous place. Signals from GPS satellites exist alongside Bluetooth headsets and the dispatch channels of police stations. The emergence of low-cost software-defined radios (SDRs) have made this world more accessible than ever. In this talk, Marc will discuss how public data can be joined with the electromagnetic spectrum to better understand the world around us. In the first portion of the talk, he will discuss how governments regulate the usage and ownership of the electromagnetic spectrum. The data residue of this process can be used for everything from geolocating electronic border surveillance infrastructure to discovering the location and transmission frequency of every McDonald's drive-thru radio. He will also discuss how various protocols for data transmission can be decoded and joined with contextual public data. For instance, every cargo ship emits an "automated identification system" signal that can be joined with shipping records to understand what the ship is carrying. Attendees will leave with a richer sense of how the radio waves are being used and the tools necessary to critically explore them further.