This file takes a very long time to download and/or process - on the order of a full minute in Firefox and Chrome on my highend Macbook Pro with a good internet connection. Of course, subsequent runs were much quicker, due to caching, but that's not the experience that new users would have. When I downloaded the JSON defining CShapes and accessed that as a file attachment, it loaded much quicker: https://observablehq.com/d/9bfbcc681392ed7b

Nice dataviz. However it's difficult to see the changes. Would be better to compare two dates on a static map.