I went tot the current (2014) end of a metro line taking me up north, far past 4Levent. I had no clue where I'd end up, and was surprised, when I got above ground, to see nothing but trees in some directions. The city being growing all the time I would not know how long the trees will remain, but for the time being this was definitely the edge of town. From a vantage point at a mosque I could see the Black See at the end of the Bosporus in the not too far distance.