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Figure 1. This BLM map depicts the principal meridians and baselines used for surveying states (colored) in the PLSS.. The following are the principal and guide meridians and base lines of the United States, with the year established and a brief summary of what areas' land surveys are based on each.
The term is almost always used to specifically refer to the parallels and meridians of latitude and longitude respectively in the geographic coordinate system. In modern usage, graticules are contrasted with grids , which display the eastings and northings of another coordinate reference system , such as Universal Transverse Mercator ...
In normal aspect, these map the central meridian and parallels as straight lines. Other meridians are curves (or possibly straight from pole to equator), regularly spaced along parallels. Conic In normal aspect, conic (or conical) projections map meridians as straight lines, and parallels as arcs of circles. Pseudoconical
Aeronautical chart on Lambert conformal conic projection with standard parallels at 33°N and 45°N. A Lambert conformal conic projection ( LCC ) is a conic map projection used for aeronautical charts , portions of the State Plane Coordinate System , and many national and regional mapping systems.
The vertical lines from pole to pole are lines of constant longitude, or meridians. The circles parallel to the equator are lines of constant latitude, or parallels. The graticule shows the latitude and longitude of points on the surface. In this example meridians are spaced at 6° intervals and parallels at 4° intervals.
Other meridians are longer than the central meridian and bow outward, away from the central meridian. Pseudocylindrical projections map parallels as straight lines. Along parallels, each point from the surface is mapped at a distance from the central meridian that is proportional to its difference in longitude from the central meridian.
The counterexamples are equirectangular and equal-area cylindrical projections (of normal aspects). These projections expand meridian-wise and parallel-wise by different ratios respectively. Thus, parallels and meridians cross rectangularly on the map, but these projections do not preserve other angles; i.e. these projections are not conformal.
A straight line on the Mercator map at angle α to the meridians is a rhumb line. When α = π / 2 or 3 π / 2 the rhumb corresponds to one of the parallels; only one, the equator, is a great circle. When α = 0 or π it corresponds to a meridian great circle (if