Latitude, Longitude and Coordinate System Grids

Horizontal Datums

Last Updated: Aug 7, 2017

Here’s how you can remember latitude and longitude:

Latitude lines run east-west and are parallel to each other. If you go further north north, latitude values increase. Finally, latitude values (Y-values) range between -90 and +90 degrees

But longitude lines run north-south. They converge at the poles. And its X-coordinates are between -180 and +180 degrees.

Latitude and longitude coordinates make up our geographic coordinate system.

Map Coordinate Systems

You can give anything on Earth latitude and longitude coordinates.

Various coordinate reference systems exist such as WGS84, NAD27 and NAD83. In each coordinate system, geodists use mathematics to give each position on Earth a unique coordinate. The field of study that measures the shape and size of the Earth is geodesy.

A geographic coordinate system defines two-dimensional coordinates based on the Earth’s surface. It has an angular unit of measure, prime meridian and datum (which contains the spheroid).

As shown in the image below, lines of longitude have X-coordinates between -180 and +180 degrees.
Longitude Coordinates
Longitude Coordinates
And on the other hand, lines of latitudes have Y-values that are between -90 and +90 degrees.
Latitude Coordinates
Latitude Coordinates

The equator is where we measure north and south. For example, everything north of the equator has positive latitude values. Whereas, everything south of the equator has negative latitude values. Most horizontal datums define a zero line at the equator.

The Greenwich Meridian (or prime meridian) is a zero line of longitude from which we measure east and west. In fact, the zero line passes through the Royal Observatory in Greenwich, England, which is why we call it what it is today. In a geographical coordinate system, the prime meridian is the line that has 0° longitude.

Most horizontal datums assign the equator as zero. The equator is where we measure north and south. Whereas, the Greenwich Meridian (or prime meridian) is a zero line of longitude from which we measure east and west.

Prime Meridian

Together, these lines provide a reference for latitude and longitude that always zig-zag into each other. This geographic grid gives unique latitude and longitude for every position on Earth.

Locate Anything on Earth with Coordinates

Coordinates are pairs (X, Y) in a two-dimensional space referenced to a horizontal datum. Whereas triplets (X, Y, Z) of points not only has position, but also has height referenced to a vertical datum. In other words, the X-value represents the horizontal position. Whereas, the Y-value represents the vertical position.

Coordinate Grid

Geographic coordinate systems use an ellipsoid to approximate all locations on the surface of the earth. Whereas, the datum defines the surface.

A horizontal datum has major axis, which is the longest diameter of an ellipse. Also, it has a minor axis, which is the shortest diameter of an ellipse. Finally, a horizontal datum has a radius that represents the position of the surface relative to the center of the earth.

What is a Coordinate Reference System?

A reference ellipsoid is the mathematical model of the shape of the Earth with the major axis along the equatorial radius. A geographic coordinate system uses longitude and latitude expressed in decimal degrees. For example, WGS 1984 and NAD 1983 are the most common datums today. Before 1983, NAD27 was the most common datum.

Globe: New York to Tokyo

Spherical coordinates (latitudes and longitudes) are often written as degrees-minutes-seconds (DMS). Minutes range from 0 to 60. For example, the geographic coordinate expressed in degrees-minutes-seconds for New York City is:

  • Latitude: 40 degrees, 42 minutes, 51 seconds N
  • Longitude: 74 degrees, 0 minutes, 21 seconds W

You can also express geographic coordinates in decimal degrees. It’s just another way to represent that same location in a different format. For example, here is New York City in decimal degrees:

  • Latitude: 40.714
  • Longitude: -74.006

The Federal Communications Commission has a DMS-Decimal converter tool that converts latitude and longitude between decimal degrees and degrees, minutes, and seconds.

Latitude, Longitude and Spherical Coordinate System Grids

When you put two coordinates together as a pair (X, Y), you can locate anything on Earth.

Latitude and longitude form our coordinate system grid.

Also, you can express coordinates in different ways. For example, you can use decimal degrees or degrees-minutes-seconds.

Thanks to our geographic coordinate, you can pinpoint any point on Earth such as GPS receivers. And this includes the spot you are reading this article right now.

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