Themes

Lord Howe, Raoul, Rapa, Madeira and some of the Azores islands in the subtropics; some Hawaiian windward coasts in the tropics. Altitude, exposure and geographic coordinates define the ultimate border. Separating climates able to keep any human races away from the mildest climates in the world for european races.
A border missing in the rest of the places that complete the top of the list.