Since my inclusion on some other running blogs (thanks Maddy, Charlie and Susan) and the Complete Running Network, I've had a number of questions about how you can also map runs across the country.
I'm using Gmap-Pedometer, a wonderful site that allows you to keep track of progress and save the route so that you can continue at a later date. So, when I have a significant distance increase from the last time I posted progress, I got into the site and just follow the path and re-save the route. Otherwise, I'd have to create the software myself which wouldn't be an easy thing.
So, why Philadelphia to LA? Why not someplace cooler with San Fran or Seattle? Well, I used to fly out of Philly all the time and I see the Philly to LA as one of those classic transcontinental flights across the country. It's not the most northern point to the most southern point, but it is a route that's flown across the country many times a day.
For details, take a look at the explanation posts.