Understanding Geographic Coordinates: Meridians and Parallels

Posted on Dec 19, 2024 in Geology

Geographic coordinates are a set of imaginary lines that can pinpoint a spot on the Earth’s surface. This set of lines corresponds to the meridians and parallels. Any item on our planet can be placed upon meeting the meridian of longitude and the parallel of latitude.

They Help Determine:

  • The location of a place on the Earth’s surface.
  • Formed by the intersection of a parallel (which tells us the latitude from 0° to 90° north or south) and a meridian (which tells us the longitude from 0º to 180º east or west).

What is the Equator?

The Equator is a circle perpendicular to the axis of Earth, equidistant from the poles, that divides the Earth into two hemispheres (north and south). Since it measures the latitude (N and S), its size is approximately 40,075 km.

Specifically

It is the imaginary line that divides Earth into two: the northern hemisphere and the southern hemisphere. It is also known as the parallel of origin (0°).

Parallel and Latitude

Parallel

Parallels correspond to imaginary circles that are drawn parallel to the line of Ecuador, always maintaining the same distance with respect to Ecuador and the other parallels, all being smaller than the Equator.

More Details on Parallels

  • Imaginary circles parallel to the Equator that reduce in size as they get closer to the poles.
  • Latitude is measured along them.
  • All points on the same parallel have the same latitude.
  • The maximum parallel is the Equator (0°), which divides Earth into two equal hemispheres.
  • Other notable parallels are the tropics (Tropic of Cancer 23º 27′ N and the Tropic of Capricorn, 23° 27′ S), which are the most remote places from the Equator where the sun in summer reaches perpendicular to the ground.
  • The Arctic Circle (66º 33′ N) and Antarctic Circle (66° 33′ S) are the places from which, in winter, the sun does not rise.

Important Points About Parallels

  • The Line of Ecuador is located midway between the poles.
  • The Equator is the great circle that divides the Earth into two hemispheres: Northern Hemisphere and Southern Hemisphere.
  • The parallels have been drawn at intervals of 10°, with the origin being the Equator. There are 90 parallels reaching 90 degrees in both the North Pole and the South Pole, so there are 180º in total.
  • Between each parallel, there are 111 kilometers of distance.

Latitude

Latitude is the angular distance between a parallel and the Equator. Being an angle, it is measured in degrees from 0º (Equator) to 90° (pole) to the north or south. Each degree is divided into 60 minutes, and each minute into 60 seconds. Along with longitude, latitude provides the two coordinates needed to locate a point on the surface.

Meridian and Longitude

Meridian

Meridians correspond to the circles that pass through the poles. The Prime Meridian has been identified as the one that passes through the Astronomical Observatory in Greenwich, England. The Prime Meridian divides the Earth into two hemispheres: the West or Western Hemisphere and the East or Eastern Hemisphere.

Important Points About Meridians

  • From the 0º meridian, 180 meridians are counted toward the west, corresponding to the Western Hemisphere, and 180 meridians east for the Eastern Hemisphere.
  • According to the above, there are 360 meridians in all.
  • The distance between meridians at the Equator is 111 kilometers.

More Details on Meridians

  • Semicircles perpendicular to the Equator, connecting both the North and South Poles.
  • Longitude is measured along them.
  • All points on the same meridian have the same longitude, as they see the sun at the same time during its course.
  • Following the rotation, the solar time is different for each meridian.
  • The reference meridian, from which longitude is measured, is the one passing through the Greenwich Observatory (0°).

Longitude

  • It is the distance in degrees between any meridian and the Greenwich Meridian, which is a universal reference point.
  • On our terrestrial sphere, the meridians are drawn every 10°.
  • Longitude is measured exclusively to the east or west.
  • As there are 180 meridians in each hemisphere, the longest that can be measured in each is 180 degrees, both eastbound and westbound.
  • Any point located on the surface of our planet is located at the intersection of a parallel (latitude) and a meridian (longitude). If you include the latitude and longitude of a place, you can get its exact location.

Therefore

Longitude is the angular distance between a meridian and the reference meridian (usually Greenwich). Being an angle, it is measured in degrees, from 0° (Greenwich) to 180º east or west. Each degree is divided into 60 minutes and each minute into 60 seconds. Next to the latitude, they are both necessary to locate a point on the surface.

Projection Systems

Projection systems are methods used to move all the items that appear on the Earth (sphere) to a flat surface (map). Among the most commonly used projection systems include:

  • Flat projection (in which the sphere is projected onto a plane),
  • Cylindrical and conical projections (in which the sphere is projected onto the surfaces of the figures).

There are over 200 projection systems, although only about 30 are commonly used. All projection systems involve a distortion of the mapping, either in the area, distances, or angles. Among the most used are the Mercator, UTM, and Peters projections.

Map Projections

A map projection or geographic projection is a graphic representation system that establishes an appropriate relationship between points on the curved surface of the Earth and a flat surface (map). These points are located with the aid of a network of meridians and parallels in the form of a mesh. The only way to avoid distortions of this projection would be using a spherical map, but in most cases, it would be too large to be useful.

Essential Features of a Projection

  • Conserves areas (equivalence)
  • Preserves angles (compliance)

Types of Map Projections

Depending on Which Point is Considered the Center of the Map

Distinctions are made between projections:

  • Polar, whose center is one of the poles;
  • Equatorial, whose center is the intersection between the line of Ecuador and a meridian; and
  • Oblique or slanted, whose center is any other point.

Cylindrical Projection

The Mercator projection, which revolutionized cartography, is cylindrical. In it, the globe is projected on a cylindrical surface. It is one of the most used, though usually in altered form, because of the large distortions it offers in high-latitude areas, which prevents the polar regions from being seen in their true proportions. It is used in the creation of some world maps.

Conic Projection

The conic projection is obtained by projecting the elements of Earth’s spherical surface on a conical surface tangent, placing the apex at the axis joining the two poles.

Azimuthal or Overhead Projection

In this case, a portion of the Earth is cast on a plane tangential to the balloon at a selected point, yielding an image similar to the view of Earth from a point inside or outside. If the projection is of the first type, it is called a gnomonic projection; if of the second type, it is called a stereographic projection. These projections provide a further distortion the greater the distance from the point of tangency of the sphere and plane.

Modified Projections

At present, most of the maps are based on modified projections or a combination of the above, sometimes with several focal points in order to correct possible distortions in selected areas, even when there are new ones in places that are given secondary importance, as are generally large expanses of sea. Among the most common include the Polyconic projection and Lambert projection, used for educational purposes, and world maps, produced using the Mollweide projection, which has the shape of an ellipse and lower distortion.

Other Classifications

Other classifications are usually set according to their main property, or the appearance of the grid: tangent, secant, transverse or oblique, or the relationship between the land surface and the map:

  • Conformal projection, if it meets the shapes of surfaces but not their sizes,
  • Equidistant projections, if they keep the actual distances between different points of the map, and
  • Equivalent projections, if they maintain the dimensions of the surfaces but not their shapes.

Conventional Projections

Generally, conventional projections were created to represent the whole world (world map) and give the idea of preserving the metric properties, seeking a balance between distortions, or simply making the world map “look good”. Most of these projections distort the shapes in the polar regions more than in Ecuador.