The original "49 Mile Drive" was a route created in 1938 by the San Francisco Downtown Association to highlight the city's beauty and to promote it as a tourist destination. The route has changed several times in the last 70 years, but most recently a user on Google Maps has plotted his own version of the 49 Mile Drive. The original route has been modified to avoid highways and to include scenic views such as the Painted Ladies at Alamo Square and Lombard Street (the "crookedest street the in the world"). It's also 10 miles longer, so I guess a more appropriate name would be the 59 Mile Drive. You can map your own scenic route using the map drawing tools found in the My Maps tab of Google Maps.