Earlier quoted context omitted.
Ah I see, I think I didn't make it clear enough that for the 3D viz there's only France and Spain that are currently supported today. I'll change the phrasing to make it clearer. I'm planning on adding more countries and features before the 12th. Thanks for the feedback!
Ok, shame, but thank you for the clarification. Just asking: what are technical constraints of implementing it for any location?
You need both accurate heights and outlines at ground level for buildings, forest, etc. OSM has outlines nearly everywhere, but height data can be missing. Without a height, it'll be inaccurate to answer "will that roof block the Sun", which is the whole point of the app. France and Spain both publish real heights, so they went first.
You also need good terrain elevation data: with the Sun only a few degrees up, a hill can hide it completely, and your own ground height counts too. Inaccurate terrain data can flatten hilltops for example, which I've seen in many cases.
So, since I want things to be accurate: it's one integration per country, and plenty of countries don't publish heights openly.
I'll be gradually adding more and more countries. I've already started working on the 2027 eclipse (https://eclipse2027times.com/), so by then it should have even more supported countries.