It spans May 1 2010 to December 31 2010; the 4.0 redesign launched August 25 of that year.
You can see searches for both sites spike at about that point in the graph - the 4.0 launch inspired a shitton of Digg traffic from people checking it out, and a shitton of Reddit traffic as the users left Digg.
Graph also ends at 2010.
It spans May 1 2010 to December 31 2010; the 4.0 redesign launched August 25 of that year.
You can see searches for both sites spike at about that point in the graph - the 4.0 launch inspired a shitton of Digg traffic from people checking it out, and a shitton of Reddit traffic as the users left Digg.