24 to 470 MHz, swept from a moving car.
On some drives, the radio stops decoding any one signal, instead sweeping the whole range with
rtl_power, measuring how much energy sits at each frequency. Stack enough of those
sweeps, and you can see which parts of the band are most busy around town: FM broadcast, aircraft radio, and
the 315 and 433 MHz bands that tire sensors and key fobs use. Each sweep is also tagged with GPS, so
eventually this can show where it's noisiest too!
The median received power in each ~19 MHz slice across every sweep. The dB values are relative, not calibrated against anything super real, so the shape is what to look at: the longer bars are the busier bands.