latitude and longitude
What are latitude and longitude?
Latitude and longitude are parameters or coordinates that help determine the location of any place on Earth. Both latitude and longitude are angles that uniquely define points on the Earth's sphere. They constitute a coordinate system or scheme to locate or identify geographic positions anywhere on the Earth's surface.
Latitudes are horizontal lines that measure distance north or south of the equator. Longitudes are vertical lines that measure east or west of the meridian in Greenwich, England. Together, latitude and longitude enable cartographers, geographers and others to locate points or places on the globe. They also show the angular distance of any place from the Earth's center. Latitude and longitude are both measured in degrees (°) and minutes (′).
The Earth's hemispheres and its equator
The Earth, which is almost spherical in shape, rotates around its vertical axis. An imaginary line that's parallel to this rotational axis would pass through the north and south poles, the northernmost and southernmost points on Earth, respectively.
An imaginary line can be drawn that's perpendicular to the Earth's vertical rotational axis and the imaginary vertical line connecting the two poles. When this horizontal line is equidistant from the north and south poles, it is the equator. The equator is a horizontal line or great circle that splits the Earth into two equal halves, one above and one below, referred to as hemispheres, with hemi meaning half.
The Northern Hemisphere is above the equator, and the Southern Hemisphere is below the equator. The equator plays an important role in geography and cartography, particularly when it comes to the measurement of latitudes and longitudes.
Latitudes are defined with respect to the equatorial reference plane. This plane passes through the center of the Earth and contains the great circle representing the equator. Latitude lines are imaginary circles that extend horizontally above and below the equator. They also run laterally from left to right. These lines, often called parallels of latitude or circles of latitude, are always parallel to the equator.
The latitude is the angle created by two connecting lines: the line connecting the latitude and the center of the Earth and the line connecting the equator with the center of the Earth. Where these two lines meet, they form an angle, which pinpoints the north-south position of a particular location on Earth.
The arc between the equator and each of the poles is 90 degrees. This refers to one-fourth the circumference of the Earth. That's why the greatest possible latitudes are 90 degrees north and 90 degrees south.
The 5 important circles of latitude
In addition to the equator, the Tropic of Cancer, Tropic of Capricorn, the Arctic Circle and the Antarctic Circle are the five circles of latitude found on almost all maps and globes.
The Tropic of Cancer marks the northernmost position on the Earth. In this position, the sun is directly overhead during the June solstice. The June solstice is the longest day of the year in the Northern Hemisphere because the Northern Hemisphere is tilted toward the sun. It is also the shortest day of the year in the Southern Hemisphere because this hemisphere is tilted away from the sun.
Similarly, the Tropic of Capricorn marks the southernmost position on the Earth, where the sun is directly overhead during the December solstice. The December solstice is the longest day of the year in the Southern Hemisphere since it is tilted toward the sun and the shortest day of the year in the Northern Hemisphere because it is tilted away from the sun.
Latitudes: Northern and southern hemispheres
A place in the Northern Hemisphere is identified by its northern latitude and assigned a suffix of N for north. The latitude of the Tropic of Cancer, which is the horizontal imaginary circle above the equator, is expressed as 23 degrees 26 minutes north, or 23° 26′ N. Similarly, the Arctic Circle, which is also a horizontal imaginary circle further above the equator and nearer to the north pole, has a latitude measure of 66 degrees 34 minutes north.
Latitudes in the Southern Hemisphere are assigned a suffix of S for south. Thus, the Tropic of Capricorn, the horizontal imaginary circle below the equator, has a latitude of 23 degrees 26 minutes south, and the Antarctic Circle, a horizontal circle further below the equator and nearer to the south pole, has a latitude measure of 66 degrees 34 minutes south. Locations north of the Arctic Circle are said to be in the Arctic Circle, while those south of the Antarctic Circle are in the Antarctic Circle.
Latitudes are also denoted by positive and negative signs depending on whether a particular latitude is north or south of the equator. Latitudes north of the equator are denoted by positive values, while those in the south are assigned negative values.
Latitude angles can range up to +90 degrees, or 90 degrees north, and down to -90 degrees, or 90 degrees south. The north and south poles each have a 90 degree angle with the equator, which is why their latitudes are expressed as 90 degrees north and 90 degrees south, respectively. In other words, latitudes of +90 and -90 degrees correspond to the north and south poles, respectively.
It's interesting to note that the Tropic of Cancer and Tropic of Capricorn have the same latitude measure. This is because they are both horizontally equidistant from the equator. The only difference is that the Tropic of Cancer is in the Northern Hemisphere, so its latitude is expressed as 23 degrees 26 minutes north, while the latitude of the Tropic of Capricorn in the Southern Hemisphere is expressed as 23 degrees 26 minutes south. The same goes for the Arctic Circle and the Antarctic Circle.
How to read latitude values
There are three different types of latitude: geocentric, astronomical and geographic. The geocentric latitude is most referenced in discussions about latitude. Expressed in degrees and minutes, and sometimes also in seconds, the geocentric latitude refers to the angle subtended by an angle at the Earth's center. It is always expressed in a north-south plane from the equator.
Thus, Cairo, which has a latitude of 30 degrees 3 minutes north subtends an angle of 30 degrees 3 minutes at the center of the globe. North indicates that Cairo is to the north of the equator and, therefore, in the Northern Hemisphere.
Dunedin, New Zealand, has a latitude of 45 degrees 52 minutes south, meaning it subtends an angle of 45 degrees 52 minutes at the center of the globe and lies in the Southern Hemisphere.
Longitudes are defined in terms of meridians, which are half-circles running from the North Pole to the South Pole. Since the Earth is almost spherical in shape, it has 360 degrees and is, therefore, divided into 360 longitudes.
Unlike latitudes, which run parallel to the equator, the vertical longitude lines or imaginary circles run in a north-south direction and, therefore, intersect with the equator. One-half of a longitudinal circle is known as a meridian. Meridians are perpendicular to the equator and to every latitude.
All longitudes are equal in length and lie in planes that pass through the Earth's axis. They meet at the poles, meaning the distance per degree of longitude at the poles is zero. Additionally, they are farthest apart at the equator, with a distance of 69.18 miles per degree of longitude at the equator.
The prime meridian
The prime meridian forms the reference point by which longitudes are defined and expressed. This line makes it possible to measure the position of a location on Earth based on the longitude.
On Earth, the prime meridian -- which, like all other latitude and longitude lines, is also imaginary -- passes through Greenwich, England. For this reason, it also called the Greenwich meridian. Thus, the prime meridian is the imaginary north-south line that passes through the north and south poles, as well as Greenwich. It has a longitude of 0 degrees. The antemeridian, which is the opposite of the prime meridian, is located on the other side of the Earth and has a longitude of 180 degrees.
Longitudes and the prime meridian are both used to define time zones. Greenwich Mean Time (GMT), also known as Coordinated Universal Time, is the standard time by which all other time zones are expressed -- for example:
- GMT + 0 = Time in Greenwich, U.K.
- GMT + 8 = China Standard Time
- GMT - 8 = Pacific Standard Time
Longitudes: Eastern and western hemispheres
While latitudes divide the Earth into the northern and southern hemispheres, the prime meridian divides the Earth into its eastern and western hemispheres. Longitudes provide the location of a place that's east or west of the prime meridian.
Like latitudes, longitudes are also measured in degrees and minutes, and sometimes in seconds. A longitude refers to the angle created by drawing the following:
- a line from the Earth's center to the intersection of the equator and the prime meridian; and
- a line from the Earth's center to any point elsewhere on the equator.
Thus, all longitudes are measured from the angle they make with the center of the Earth based on the intersection of the equator and the prime meridian.
How to read longitude values
All longitudes other than the prime meridian are measured by up to 180 degrees both east and west of the prime meridian.
For example, the longitude of Los Angeles is 118 degrees 15 minutes west. This indicates that Los Angeles is 118 degrees and 15 minutes to the west of the prime meridian. The longitude of Mumbai, India, is 72 degrees 50 minutes east, indicating that Mumbai is 72 degrees and 50 minutes to the east of the prime meridian. So, Los Angeles is in the Western Hemisphere, and Mumbai is in the Eastern Hemisphere.
How to read both latitudes and longitudes
Every location on Earth is expressed in terms of its latitude and longitude values. Together, the circles of latitude and meridians of longitude show where a particular place is located on Earth with reference to the prime meridian and the equator.
A point described as 59 degrees 57 minutes north and 10 degrees 45 minutes east is located 59 degrees and 57 minutes north of the equator and 10 degrees and 45 minutes east of the Greenwich meridian. This location is Oslo, Norway.
Montreal, Canada is expressed as 45 degrees 30 minutes north and 73 degrees 34 minutes west. These coordinates show that Montreal is 45 degrees 30 minutes north of the equator and 73 degrees 34 minutes west of the prime meridian.
Papua New Guinea is in the southern and eastern hemispheres. That's why the coordinates of its capital city, Port Moresby, are expressed as 9 degrees 31 minutes south and 147 and 13 minutes east.
The coordinates for Macapá, Brazil, are 0 degrees 2 minutes north and 51 degrees 4 minutes west. The 0 indicates that Macapá is close to the equator, albeit in the Northern Hemisphere (2 minutes). It is also located to the west of the prime meridian.
Brazil is one of the few countries in the world that lies in both the northern and southern hemispheres. For example, Belém is located at 1 degree 27 minutes south and 48 degrees 30 minutes west, which shows that Belém is in the Southern Hemisphere and below the equator.
Several countries have both northern and southern latitude circles, i.e., they lie in both the northern and southern hemispheres:
Similarly, a few countries are in both the eastern and western hemispheres, so they have both east and west longitudinal coordinates:
- Burkina Faso
The Greenwich meridian passes through the United Kingdom, and it lies in both the eastern and western hemispheres. The only country in the world that lies in all four hemispheres is Kiribati.
See also: Global Positioning System, GPS navigation system, GPS coordinates, location-based service and spatial data.