Mid May I fly into Washington DC to begin my ride to Portland, Oregon, but first, to make it official, I need to ride another 120 or so miles to the Atlantic.
Make it Official? It's your ride. Start it where it suits you. I counted my DC to San Francisco ride as a coast to coast as the Potomac River in Washington is tidal.
From DC the C&O Canal and GAP trail followed by the Old Lincoln Highway give an easy to follow and high quality route west for the first few hundred miles.
Aside from the coast or tidal river argument a capital city is a nice place to start a tour. There are not many capitals with a continuous traffic free route starting right in the downtown area like the C&O