I stumbled upon this article last night on philly.curbed.com that takes a look at the growth and slowdown in said growth in Philadelphia. For the purposes of this blog, that included an animated .gif that showed the expansion in the metro area since the 1940s.
My quibble with the piece is that the lighter blue loses out to the darker. And so one really sees the presence of the city at the expense of the growth. I wonder if reversing the two colours or in some other way de-emphasising the areas built up would allow the new growth areas to come to the forefront of the map.
Credit for the piece goes to BuildZoom.