Reddit user bistromat has recently updated the GNU Radio based Mode S ADS-B decoder gr-air-modes. He has added Google maps view, a legend and zoom support to the azimuth map view, and has restructured the underlying code. The new gr-air-modes requires the latest GNU Radio 3.7 version.

Check out the original post here (with cute puppy included), and clone the latest version via github from the following link.

https://github.com/bistromath/gr-air-modes