This example shows the use of a legend to display a quantized threshold key. Inspiration comes from the need to describe the colors of a Choropleth in limited horizontal space. The legend box allows stacking of blocks to represent the hues. With limited space comes the possible need to split the title into two (or more) lines.
In D.C. Choropleth, I used a variation on Bostock’s Threshold Key to show quantized colors. That particular diagram had quite a bit of empty space when displayed in a 960px wide block. With this “legendary” key, it can be shown in a block half as wide.