Imagine living on islands where the absolute highest point is 10ft above sea level.

I read the title as “highest priority of every country in the world” and that would be kinda cool to see!

The government's highest priority or the highest priority of its citizens?

Both would be interesting. When I read it wrong at first, I guess I imagined the government’s because when I thought of the US, I guessed “security.”

Oh, this is actually pretty beautiful for a change

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The colour scheme is awful. Why not just use a constant gradient with pale for lowest and dark for highest?

And that's probably 13 feet at low tide, 7 feet at high tide.