An experiment with encoding the change over time of a value in a treemap. Each rectangle represents the imports to the United States from the countries shown in 2015. Within each rectangle, the "corners" from a rectangle of the same ratio are drawn according to the value of imports from an earlier decade (2005, 1995, 1985) and these corners are connected to form a vector of change. This works pretty well for progressive growth. It "overflows" a bit when an earlier value is higher than the current but other than that it suffers a bit for representing change that's negative.
Found the data for this chart via cmgiven's cool Treemap Bar Chart
Data Sources: Census