Server-side generated heightmap

Hello to everybody !
I'm new to Unity and I'm totally lost in what I'm trying to achieve :
I have a PHP server generating a 16x16 cells grid, corresponding to 1 terrain chunk (an entire island in my game, low-poly terrain is fine.).
I want my script to dynamically load the grid from the server as a JSON object and create a new Terrain object with the values from the loaded grid.
I'm already stuck with the 'loading raw data from server' part because I use :

    var www = WWW("http://localhost/unity_network/simpleTerrain.php");

    yield www ;

Thanks for your help !