>>Are you saying they were all wrong in basing these classifications on whole continents?
>
>I find continents an inexact location system. Sorry.

Whole geography is inexact, but we make do with what we have. The sufficiently large pieces of land were named as continents some (20?) centuries ago, imaginary lines were drawn, and it's a given that the whole world adheres to these names. Strictly speaking, there should be only four continents - Eurasiafrica (because they are connected by land), America (North and South connected), Australia and Antarctica. But, as I said, lines were drawn and remained so in the eyes of the whole world.

>What continent is Mexico on?

North American. IIRC, the division line is the Panama Canal or thereabouts.