Atlanta and Boston are about 936 miles apart by road. Split the difference and you arrive near Richmond, the city closest to the halfway point between them. That splits the trip almost evenly — about 9 hr 51 min from Atlanta and 9 hr 56 min from Boston.
Over this distance most people will fly rather than drive the whole way. Richmond still makes a fair, central place for Atlanta and Boston to converge, splitting the travel instead of asking one side to cross the country.
If Richmond doesn't have what you're after, Washington and Raleigh are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Atlanta and Boston.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.