You might find that obj’s dump1090-mutability already has significant improvements over the FlightAware-supplied dump1090, both in functionality and web page design. See http://discussions.flightaware.com/ads-b-flight-tracking-f21/raspbian-ubuntu-packages-for-dump1090-mutability-available-t19619.html for details. Perhaps you could make this your starting point. With this, the gmap.html file is here: /usr/share/dump1090-mutability/html/gmap.html