The transparency thing should work. You need to work with the Alpha channel for the negative spaces & not a grayscale image. Try "invert image" in the shader control for mapping style. Another you could do is make the model for the arch in the spline modeler. Best way to do that is start with Illustrater (or Similar vector drawing app) and imoprt image as a template. Then draw your bezier curves, outlines & shapes for negative areas. Trash the image & save as eps. Go to CAR spline modeler & then "import eps file" to cross section. Select negative spaces and outline & "combine as compound" and you will end up with the archway with holes in it to the correct proportions for the map Except in the depth. Just reduce the depth scale Or change it in the spline modeler extrusion length plane.