New Zealand is a problematic place, it doesn't show up on a lot of maps so people from there need to know how far off Australia to travel to get back, a fair amount of them have natural distance measuring abilities. That is what they mean by being your ruler.

Having lived in New Zealand and Oregon, I wish Oregon was on less maps.

Lorde is actually more of an anthropomorphic bendy tape measurer, which lends them to more forms of metrology than we give them credit for. They aren't just pop icons. They're people. When they aren't rulers.