It's a map, not a graph so there is no y-axis. The colored area represents the size of the army with the gold area being March to Moscow and the black being th

It's a map, not a graph so there is no y-axis. The colored area represents the size of the army with the gold area being March to Moscow and the black being the retreat. There were two small groups that split from the main thrust. The black are them rejoining the retreat. As you can see you were luck if you were in one of those two groups since they did not get decimated.