Using Aerial Photos for Terrain Mesh

I've been attempting to combine several B& W aerial photos of my area to use as the texture to drape over the default mesh. (At least that's what i think i'm doing)I combined multiple Source entries in the inf file to make 1 bgl file.I used PhotoScenery maker and Terrabuilder and even the MSFS 04 SDK tools. The photos have combined well into one large photo texture. The only problem i can't solve is the blue"water" texture around the perimeter of the large photo texture(for lack of better terms)I'm aware that the outer edges of the photo which don't fill a terrain cell leave a black area, possibly an alpha channel, which msfs sees as water.i've tried the NorthLon, NorthLat commands in the Destination, hoping to match the exact coords of the terrain cells, but it doesn't work. Is there a post about this?Also, in my same area, which is mountainous, is there a way, to level out a flat area along the hillside to put a small airstrip in?