The height of each state represents the population density while the volume of the figure represents the state's total population. To obtain the height, the population per square mile was multiplied by 1,000 to get the height in meters.
The Northeast US has many densely populated states, including New Jersey, the most dense of them all. The high yellow bar is the District of Columbia, but it does not qualify as a state.
Illinois is the most populated state in the Midwest.
Alaska is so sparse that it barely registers any height.
We see Hawaii and some West Coast States.