Thanks Mouse !

You wanna know the secret ? Use an overlay or soft light layer, take a soft brush at low opacity and go crazy. Some parts may look awful, too bright or too dark. Go over the light parts with black and over the dark parts with white to finally get what you want and if it's too much, use an eraser at low opacity. I ended up with a layer with way too much contrast so I just decreased the opacity of the layer. Once again, for a good reference on top-down maps, go there He's a king !