Web mapping has come a long way in the last five years. Back then, all the best interactive maps were mashups – informative but clunky overlays made with Google or OpenStreetMap, with limited potential for customization and interactivity. Flash forward and today's best maps are being made with D3, a JavaScript library that uses the full potential of the web to animate, transform, and decorate. Maybe you don't know anything about D3. But if you love maps, you should.