Graticule
A graticule is a network of geographic lines. We use it to refer to the rectangular[1] 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
- ^ 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 trapezium. In the limit, at the north and south poles, the graticules become triangular. 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. On the Mercator projection used by Google Maps however, the earth is distorted so that the shape is, in fact, rectangular.
