There is no out of the box map chart in Coda but there’s a few ways you can achieve it.
First is that you can render it locally in Coda with the help of SVG. You can try implementing it yourself or we can ask @Quentin_Morel who used this trick to render all sorts of charts, including the map of his country France — maybe he’ll share his doc and instruct you how to replace France with the US.
P.S. Ah actually he’s got a doc for it already with the US map. I knew I had seen it!
Second is that this whole thing can be wrapped in a pack. If only I had more time I’d do it myself, and maybe one day I will. It can be anything as simple as wrapping this trick and just render a non-interactive SVG, up to something complicated like a pack for a whole 3rd party charting library (Highcharts etc.) Again, had ambitions myself but no resource to build it all.