Geography was always my worst academic subject at school, maps confound me :) I mean it's not completely arbitrary, the boundaries between say North and South America seem relatively unambiguous (unless you live in Panama I suppose) It's much less arbitrary than grouping countries by alphabetical order or something. But it's not as intuitive to me as a non-geographer as some other divisions might be.

Though as I recall the last time I did a poll like this the options were "Australia" and "Other" :D