The equator is a line going around Earth and is halfway between the North and South Poles, it is given a latitude of 0°. Values increase north of the equator and are considered positive and values south of the equator decrease and are sometimes considered negative or have south attached to them. For example, if a latitude of 30°N was given, this would mean that it was north of the equator. The latitude -30° or 30°S is a location south of the equator. On a map, these are the lines running horizontally from east-west.
Latitude lines are also sometimes called parallels because they are parallel and equidistant from each other. Each degree of latitude is about 69 miles (111 km) apart. The degree measure of latitude is the name of the angle from the equator while the parallel names the actual line along which degree points are measured. For example, 45°N latitude is the angle of latitude between the equator and the 45th parallel (it is also halfway between the equator and the North Pole). The 45th parallel is the line along which all latitudinal values are 45°. The line is also parallel to the 46th and 44th parallels.
Like the equator, parallels are also considered circles of latitude or lines that circle the entire Earth. Since the equator divides the Earth into two equal halves and its center coincides with that of the Earth, it is the only line of latitude that is a great circle while all other parallels are small circles.
Development of Latitudinal MeasurementsSince ancient times, people have tried to come up with reliable systems with which to measure their location on Earth. For centuries, both Greek and Chinese scientists attempted several different methods but a reliable one did not develop until the ancient Greek geographer, astronomer and mathematician, Ptolemy, created a grid system for the Earth. To do this, he divided a circle into 360°. Each degree comprised 60 minutes (60') and each minute comprised 60 seconds (60''). He then applied this method to Earth's surface and located places with degrees, minutes and seconds and published the coordinates in his book Geography.
Although this was the best attempt at defining the location of places on Earth at the time, the precise length of a degree of latitude was unresolved for around 17 centuries. In the middle ages, the system was finally fully developed and implemented with a degree being 69 miles (111 km) and with coordinates being written in degrees with the symbol °. Minutes and seconds are written with ', and '', respectively.
Measuring LatitudeToday, latitude is still measured in degrees, minutes and seconds. A degree of latitude is still around 69 miles (111 km) while a minute is approximately 1.15 miles (1.85 km). A second of latitude is just over 100 feet (30 m). Paris, France for example has a coordinate of 48°51'24''N. The 48° indicates that it lies near the 48th parallel while the minutes and seconds indicate just how close it is to that line. The N shows that it is north of the equator.
In addition to degrees, minutes and seconds, latitude can also be measured using decimal degrees. Paris' location in this format looks like, 48.856°. Both formats are correct, although degrees, minutes and seconds is the most common format for latitude. Both however can be converted between each other and allow people to locate places on Earth to within inches.
One nautical mile, a mile type used by sailors and navigators in the shipping and aviation industries, represents one minute of latitude. Parallels of latitude are approximately 60 nautical (nm) apart.
Finally, areas described as having low latitude are those with lower coordinates or are closer to the equator while those with high latitudes have high coordinates and are far. For example, the Arctic Circle, which has a high latitude is at 66°32'N. Bogota, Columbia with its latitude of 4°35'53''N is at a low latitude.
Important Lines of LatitudeWhen studying latitude, there are three significant lines to remember. The first of these is the equator. The equator, located at 0°, is the longest line of latitude on Earth at 24,901.55 miles (40,075.16 km). It is significant because it is the exact center of the Earth and it divides that Earth into the Northern and Southern Hemispheres. It also receives the most direct sunlight on the two equinoxes.
At 23.5°N is the Tropic of Cancer. It runs through Mexico, Egypt, Saudi Arabia, India and southern China. The Tropic of Capricorn is at 23.5°S and it runs through Chile, Southern Brazil, South Africa and Australia. These two parallels are significant because they receive direct sun on the two solstices. In addition, the area between the two lines is the area known as the tropics. This region does not experience seasons and is normally warm and wet in its climate.
Finally, the Arctic Circle and Antarctic Circle are also important lines of latitude. They are at 66°32'N and 66°32'S. The climates of these locations is harsh and Antarctica is the largest desert in the world. These are also the only places that experience 24 hour sunlight and 24 hour darkness in the world.
Importance of LatitudeBesides making it easier for one to locate different places on Earth, latitude is important to geography because it helps navigation and researchers understand the various patterns seen on Earth. High latitudes for example have very different climates than low latitudes. In the Arctic it is much colder and drier than in the tropics. This is a direct result of the unequal distribution of solar insolation between the equator and the rest of the Earth.
Increasingly, latitude also results in extreme seasonal differences in climate because sunlight and sun angle vary at different times of the year depending on latitude. This affects temperature and the types of flora and fauna that can live in an area. Tropical rainforests for example are the most biodiverse places in the world while harsh conditions in the Arctic and Antarctic make it difficult for many species to survive.
Take a look at this simple map of latitude and longitude.