graticule

A graticule is a network of lines on a map or globe that represents geographic coordinates. It is formed by parallels of latitude and meridians of longitude, whose intersections define a grid. Latitudes run parallel to the equator, while longitudes are half-great-circles that converge at the poles. The term derives from Latin graticula, meaning a small grid or lattice.

On a globe the graticule reflects true geometry, but on a map produced by a projection the lines become curved and the grid distorts with distance and angle. Graticule lines can be drawn at regular intervals, commonly 1 degree or 5 degrees, depending on the map’s scale and purpose.

Applications of the graticule include providing a reference system for locating places, measuring distances, and overlaying spatial data in cartography and geographic information systems. It aids navigation and education, and in astronomy the concept extends to the celestial sphere with grids such as declination and right ascension, sometimes referred to as a celestial graticule.

A related use of the term appears in optics and microscopy, where a graticule (reticle) is a transparent grid in an eyepiece used for measurement or alignment.