I think it is assumed that whomever is reading knows how to program an animation using their choice of framework/library/whatever, and that the most common meth

I think it is assumed that whomever is reading knows how to program an animation using their choice of framework/library/whatever, and that the most common method for dealing with these is pixels in a grid. So, the budding game developer (the audience), knows that a pair of numbers (x,y) are used to represent position. Indeed, most hello-world style tutorials for SDL, Allegro, GameMaker etc are concerned with getting something on the screen at a certain location.