Blonde Roots is a satire. It's not supposed to make literal sense. I've got a half-written review that I should really finish, but I loved it, right down to the anachronisms.

The map at the front... Eh, I could have lived without that. I liked the point of the map -- essentially separating the British Empire from the ethnic English, Scottish, and Welsh, so that she can do the reversed-roles satire without letting the Empire off the hook for its colonial and slaving history, but the map that she used to express that was both painful to look at and made pretty much unnecessary by the text.