The equator is geographically significant, yes, but it mainly just is another invisible line on our map. You could center a equirectangular map anywhere in the world, effectively treating any great circle (or really, any circle at all!) as the equator and any two points as poles- here we see the cassini projection of our world:
cassini_blank.png
Which is basically the equirectangular projection with the prime meridian as the equator (it is called a cassini projection, just like how a plate careé is just an equirectangular projection centered on the equator).
(I agree with you that it is anachronisctic, but we can make exceptions in order to provide our readers/players/others clearer maps.)