When you first enter the city, on the way to your objective, you are forced to stop in the Coventry district to deal with a signal coming from a Comms Tower which is jamming your ability to use the Batwing Drop Points (fast travel).
Once you do so ten Network Relays are marked on your map. Set a waypoint on a Relay with the Y button and it appears on your compass as a light blue hexagon with an exclamation point (!) in the middle. It will also become your new objective marker which is the Bat Signal with the arrows of light below it.
Once you arrive the Relay can be easily found using Detective Vision (LB). It will be highlighted and have a visible signal effect. Take it out with the Batarang (down on the D-pad and either tap LT or hold LT to aim and RT to throw) and move on to the next. Once all ten are destroyed the achievement is yours.