Graticule

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A graticule is a network of geographic lines. We use it to refer to the rectangular¹ zones between the latitude and longitude lines, each 1°×1° in size.

Shape

The shape and size of a graticule as measured over the ground (in miles or kilometers) varies with distance from the equator. A graticule near the equator (latitude 0) is almost exactly square shaped (roughly 111×111 km or about 69×69 miles); other graticules are still 111 km in north-south direction, but become narrower and narrower as one goes further away from the equator. For example, the Groningen graticule, at +53° latitude, is roughly 67 km in the east-west direction. Graticules touching on the North Pole (or the South Pole) actually have the shape of a piece of pie, since the northern (southern) border of such a graticule has length 0. Google maps, however, does not cover latitudes below -85° or above +85°.

Numbering

Graticules are numbered with a pair of numbers based on the corner closest to N0°, E0°, so that the graticule a location belongs to can be determined by truncating the degree fraction.

Note that in this numbering 0 is not the same as -0: graticules immediately west of the Greenwich meridian have the east/west part -0°, and graticules immediately south of the equator have the north/south part -0°. For example, graticule (52, 0) is Cambridge, United Kingdom, whereas graticule (52, -0) is the next graticule westwards, Northampton, United Kingdom.

Footnotes

1: It isn't entirely true that the graticules mark out a rectangular chunk of ground. The side of the graticule closer to the equator will be larger than the one closer to the pole, leading to something more akin to a trapesium. Add to this the additional complexity of the curvature of the earth and any discussion of the shape of a graticule is either hideously technical or an oversimplification.

However, on the Mercator projection used by Google Maps, the earth is distorted so that the shape is, in fact, rectangular.