You can see the Horizon "Aircraft Tracking" Insight application in the Horizon Unified Map, here:
You should see something like this:
On that global map you will see blue and gray dots for each device participating in one of Horizon's Insight applications. Blue dots represent devices on Horizon that have recently sent data. Gray dots represent devices that have sent data at some previous time. (Gray dots represent inactive devices which may be permanently shut down, or perhaps are just temporarily severed from their network connections.) Note also that the top left menu allows you to select only dots that are participating in specific Horizon experiments. You may also select whether or not to show inactive dots, and whether or not to show live aircraft tracking on the map.
Horizon Device Map
To see planes on the map, select the "planes" item at the bottom of the Insight menu. (You can optionally uncheck the other items to reduce clutter on the map.) You should now start seeing live aircraft tracking on the map. If you tap any of the aircraft, you will see the historical data captured for that aircraft (i.e., a line showing previously collected location information for that plane as shown in the screen capture below). The selected aircraft appears to be on its approach to one of the airports in the San Francisco Bay area from some origin point to the east. If you double-tap an aircraft, you will see details about that aircraft (altitude, speed, etc.)
Of course, aircraft can only be tracked by participating Horizon edge devices with Software Defined Radio hardware. Also the range across which those devices can receive the aircraft's ADS-B transponder signals will vary widely with terrain, antenna position, antenna quality and tuning, etc.
The Aircraft Tracking Insight application has a relatively simple architecture consisting of a centralized web server where the data is aggregated and served as a Google map page, and many individual edge devices that both have the appropriate Software Defined Radio hardware and are running the Horizon Aircraft Tracking code (in a Docker container). The components involved are illustrated in the diagrams below: