When I was taking graphic design history we looked at all these posters.  I would have to say that the way the layout is in a grid pattern.  With the people in the middle of the poster really set off the letters and the people makes it followable.  From the hand of the lady with the fan it flows in a c shape to her foot which makes for an easy line to follow.  The place is important so it is in a bold  and big so it can be seen.