To date, there are only a few dozens of cities that can be used in this mode. Note that Apple has not merely intramural Paris: the area covered by 3D extends to Versailles, to Aulnay-sous-Bois, to Disneyland Paris and to The Hay-les-Roses.
In March, Apple revealed numerous improvements to Maps via the Loop, including Flyover support for many new cities in the USA.
Take a look at a couple sample shots below...
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