This is a great one. Today, the data behind your choropleth map updates. What do you do? Press refresh. The palette and the areas all change.
But if you’ve hand-shaded that map? What do you do? Use the system above!
You can use pins for the dots, or ink, and represent changing density on the same map each time you update it.
Brinton does point out that if you use ink for this, you’re stuck if density DECREASES: you can’t remove ink!