I came across this recently:
“SPLAT! is a powerful terrestrial RF propagation and terrain analysis tool covering the spectrum between 20 MHz and 20 GHz. SPLAT! is free (GPL) software, and is designed for operation on Unix and Linux. Applications of SPLAT! include the visualization, design,and link budget analysis of wireless Wide Area Networks (WANs), microwave links, and the determination of radio and television contour regions.
SPLAT! produces reports, graphs, and high resolution topographic maps that depict line-of-sight paths, and regional path loss contours through which expected coverage areas of transmitters and repeater systems can be obtained.” (end part quote)
It’s a command line facility, that produces PNG, PPM format files for viewing. It also can produce KML files, which you can use to “fly over” a path with Google Earth! (Beware though – KML files if published give everyone an exact picture of where your site is!).
It seems like a very useful tool, and uses readily available terrain data for the mapping.
It is available at http://www.qsl.net/kd2bd/software.html
Steve