In this Equal Earth projection, lines of latitude (parallels) are shown as horizontal red lines and lines of longitude (meridians) are displayed as vertical green lines. The thick red line represents the Equator at 0° latitude, and the thick green line represents the Prime Meridian at 0° longitude.
Latitude
Latitude describes the horizontal lines (called parallels) on a map or globe that measure the angular distance north or south of the Equator. Latitude values range from 0° at the Equator to 90° at the poles. These lines are evenly spaced and parallel to each other, making them useful for determining a location's position along the north-south axis. Locations in the Northern Hemisphere are labeled with N or indicated as a positive value (e.g., 45°N or 45° for a point 45 degrees north of the Equator), while those in the Southern Hemisphere are labeled with S or indicated as a negative value (e.g., 30°S or -30° for a point 30 degrees south of the Equator).
The Central Parallel is the line of latitude around which a map projection is centered. It typically corresponds to 0° latitude (the Equator), but it can be adjusted to re-center the map on a different region. For instance, in polar maps using certain projections (e.g., azimuthal equal area or stereographic), latitudinal rotation can be adjusted by 90 degrees to center the map appropriately.
Some projections, such as the Conic Conformal projection, minimize distortion at particular latitudes, called standard parallels (dashed lines). In this case, the standard parallels are set at 20°N and 50°N.
Standard Parallels are lines of latitude used in conic or cylindrical projections to define where the projection intersects the globe. These parallels minimize distortion in the areas near them, ensuring the map is most accurate for regions between or close to these lines. For example, the Conic Equal Area projection is often optimized for the contiguous United States by setting the standard parallels to 29.5°N and 45.5°N, a configuration known as the Albers projection.
Longitude
Longitude refers to the vertical lines (called meridians) on a map or globe that measure the angular distance east or west of the Prime Meridian, which is set at 0° longitude and runs through Greenwich, England. Unlike latitude lines, meridians converge at the poles and are widest apart at the Equator. Longitude values range from 0° at the Prime Meridian to 180 degrees east (180°E or 180°) or 180 degrees west (180°W or -180°), determining a location's position along the east-west axis. For example, a point 90 degrees east of Greenwich is labeled 90°E, while a point 45 degrees west is labeled 45°W.
The Central Meridian is the line of longitude that serves as the center of a map projection. For example, in the Mercator projection, the central meridian often corresponds to 0° longitude (the Prime Meridian), but it can be adjusted to re-center the map on a different region.
Graticules
Graticules are the grid lines formed by the lines of latitude (parallels) and longitude (meridians) on a map. These lines are typically evenly spaced, allowing for consistent intervals such as every 10° or 20°, and they serve as a visual reference for geographic coordinates. Graticules help convey spatial relationships and make it easier to interpret locations on the map. In Mappica, graticules can be toggled on or off using the toolbar while previewing a basemap.
