I have found an easy way to get this achievement that requires no upgrades of any kind, and can be done as soon as the game allows you to free-roam. What you need to do is head to the Merchant's Bridge (where the first mutilated body can be found). Climb to the top of the bridge's supports, which has you about 60 meters off the ground. Dive bomb from there to the street surface, then even out over the cars, heading south. Glide 200 meters or more, without ever straying above 10 meters from the road surface. This route can be tricky, as the street starts to curve downward (because you're gliding over a ramp/slope), so you must follow the curvature of the road without ever hitting the floor.
Using this method, I was able to glide almost 400 meters in one tilt, with no upgrades to my gliding, grapnel hook, or anything else aiding traversal. The fact that the road you are gliding over tilts downward adds almost 150 meters of distance on it's own, which you'll never actually hit the road unless you make an error on the joystick (Batman won't naturally sink to the street as it's curving away from him). At the end of the glide, you should end up about here.