Nice map! (But for some reason the azimuthal equal-area projection is really bugging me. I wonder if we could figure out a better one for the region shown.)

I like the updated arrow start style and swoopy arrow shafts on the final wapo maps. Are those done automatically or just manually drawn? Arrowheads on the final map are also great. If you ever have trouble finding just the right arrowhead... https://observablehq.com/@jrus/arrowheads

Thanks for taking a look and all the feedback! You're correct, a lot of the final styles were manually adjusted for the map that published. Also, this arrowheads notebook is SO COOL. It's definitely going to come in handy, thank you.

Hey Atthar. I love the final graphic you shared. I've just taken a pop at creating a similar layout in this fork https://observablehq.com/@bayre/spatially-situated-sankey

Wow, this is INCREDIBLY cool. I'm still relatively new at D3 and had no idea a sankey diagram was even possible. I'm so impressed!!! Definitely going to be examining your notebook in detail, I can't thank you enough for making it.

It's a bit of a hack really! Glad you like it :)