By default Dump1090 interface will not display the distance between an aircraft and the site this can be easily corrected by editing a single file and providing the latitude and longitude where the receiver(yours) is located. The file in question can be located for Dump1090-mutability at
Before we can start editing the configuration file first we need to obtain the latitude and longitude of the site as I assume you don’t know this information I suggest using Google Maps to obtain it. Visit google.com/maps search for the address where the receiver is located. Once you find the site(address) right click on the location to display the menu and select What’s here? Near the bottom of the window you should see the latitude and longitude of the site displayed. Copy this information exactly the way it appears. My installation runs on a Raspberry Pi 2, log in to the system where Dump1090 runs and with enough permission look for and edit the following parameters LAT= latitude, LON=longitude this are the parameters well be adding the latitude and longitude information to.
sudo nano /etc/default/dump1090-mutability
\# If set, supplies a reference location for local position decoding.
We are almost done now just reboot dump1090.
sudo service dump1090-mutability restart
Dump1090-mutability should start reporting the distance.