katie or kate

i've noticed recently a growing number of people calling me kate. i would guess that since i've moved to halifax, most of the new people i've met call me kate. i introduce myself as katie, however it gets stored in their memory as kate. why? i'm finding it quite odd, especially as some older friends and family members are doing it now too. surely 'katie' isn't THAT long and difficult to pronounce. i don't mind it. in fact i sort of like it but i just don't understand the sudden shift. is katie a little girl's name? do i look like a kate more than a katie? is it the short hair?
any thoughts?