An interesting visualisation – history of a growing United States – mapping built using R. 

The animated map above shows population density by decade, going back to 1790 and up to recent estimates for 2015. The time in between each time period represents a smoothed transition. This is approximate, but it gives a better idea of how the distribution of population changed.

The Data used for this mapping is from the Census Bureau amd made better accessible by NHGIS.