I work for a land planning firm. - I have a map (aerial) of an area. - I have several PNG files that depict various land planning principles (like, dashed lines over the roads, certain colors for certain building types, etc.) I'd like to have an app, like Google Earth, that allows multi-touch (pan, tilt, zoom), that allows me to overlay these separate PNG files on top of the underlying aerial. It'd be great if I could toggle the layers easily "on and off" OR change the opacity of individual layers. Thoughts?