GPS and APRS Applications
There are two wonderful GPS programs, one is specific for OS X and the other is open source, multi platform.
The first is MacGPSPro and is a solid mapping application.
The second is Xastir. This is primarily used for APRS and again is a solid program. The mapping functions in Xastir are spectacular, utilizing many sources for maps. Most people use TIGER maps. Xastir is also run in Terminal, like QCar.
I got into the idea of putting my Mac in my Land Rover to use Xastir with my Ham Radio and the APRS functions. Getting all the other stuff, is icing on the cake.
Have you thought about integrating a mapping software that utilizes USGS maps and not just road maps?