Why latitude surprises
Latitude is the plainest of coordinates: how far a place lies north or south of the equator, from 0° on the equator to 90° at each pole. Every place on one line of latitude is exactly as far from the equator as every other place on it, whatever the continent, the coast or the weather.
Our mental maps rarely work like that. We picture a city through what we know of it, its seasons, its sea, its corner of the world, and slot it onto the globe by feel. Lay a straight line across the map and the feel falls apart. London sits at 51.51° N, a little north of Calgary at 51.05° N. Rome, at 41.89° N, is further north than New York City, at 40.71° N.
The line is also a good way to meet places you rarely think about together. In our list of 382 cities, Longyearbyen is the furthest north, at 78.22° N, and Ushuaia the furthest south, at 54.81° S. Of the 382, 313 lie north of the equator. The busiest line is 39.5° N, with 22 cities within 1° of it.
How to read the map
The map uses an equirectangular projection: every degree of latitude is drawn the same height, so each line of latitude is a straight line across the map and the band of 1° either side of it, about 220 km from edge to edge, is the same thickness everywhere. The price is that land is stretched sideways more and more the further it lies from the equator. Distances on this page are north to south only, at 111.2 km per degree of latitude; they are not travel distances.