Now that we understand the shape and size of our planet, let’s consider the difficult challenge of measuring and describing points thereon. How, for example, do we tell someone who lives on the other side of the Earth where another object is located? Suppose that we are in an unfamiliar land and we need to find a distant but important object that is hidden somewhere else on the Earth. If we just start walking in a random direction, are we likely to find the hidden object?

In order to both study and navigate the Earth, it is important to have a system for describing locations accurately and mathematically. This system must be generally accepted by everyone, and it must be easy to use and understand.

The simplest method for describing locations either on a planet, or on any flat object, is to create a grid. A grid is a series of evenly spaced imaginary lines that intersect with one another at right angles. One set of lines are distributed across the globe horizontally, and one set of lines are distributed vertically.

But wait a moment. How do we know where the top and bottom of the Earth are? Think about it. If the Earth is round, what point is the top? Let’s consider a white marble. Where is the top of the marble? No matter which way you turn it, every side of the marble looks the same. But what happens when you spin the marble? As the marble spins, or rotates, for a few moments, there is a clearly defined top that remains pointing upwards.

Because the Earth is rotating around an imaginary axis, we can define a top and bottom. We call these the poles. Having a top and bottom of the Earth allows us to then draw the imaginary lines that we need for our grid. The lines that extend from pole to pole are called longitude, while the lines that circle the globe horizontally are referred to as latitude.

Latitude

Latitude is the angular distance of any object from the equator measured in degrees. The angular distance from the equator to itself is 0, thus the latitude at the equator is 0 °. If we move either up or down from the equator, our distance increases, and so does our angle to it. Eventually we reach either the North or South Pole. Standing on the these poles, places us at exactly a 90 ° angle to the equator.

At any location on Earth we can draw a circle around it, representing every point that is at the same latitude. If we were to cut the earth in half at the equator and place a large piece of paper in between the two halves, we would find that both halves were exactly the same size. As we move either up or down the Earth, cutting the planet into two pieces produces one large piece and one small piece. As we approach the poles, the large piece gets very big, while the small piece becomes much smaller. Drawing these imaginary lines at different latitudes produces what we call parallels. Although technically it is possible to draw an infinite number of parallels at any number of latitudes, there are a few which are important for you to understand as you study our planet.

The first of these is called the equator. The equator is located at 0 ° latitude. Going north from the equator we find the Tropic of Cancer. This parallel is located at 23.5 ° north. Continuing further northward we reach the Arctic Circle at 66.5 ° north. Continuing all the way to the top of the Earth at 90 ° latitude we encounter the North Pole. If we journey southward from the equator we will find the Tropic of Capricorn at 23.5 ° south. Continuing south we reach the Antarctic Circle at 66.5 ° south. Finally, at 90 ° south, we find the South Pole.

Longitude

As we have already read, the lines extending around the Earth horizontally are called lines of latitude. They measure how far north or south an object is on the Earth. The lines running vertically around the Earth are called longitude. These lines are called meridians, and measure how far east or west an object is.

As with latitude, longitude is measured as an angular distance. With latitude, the angular distance is measured from the equator. This is a natural place to begin. However, with longitude there is no natural beginning point. One of these lines must be designated as a prime meridian, or as the 0 ° mark, but which one? For many years, each country had its own prime meridian. France used a meridian passing through Paris, while England used a meridian passing through Greenwich, England. Either one worked just as well, as long as you were only communicating with people from the same country. But what happens as technologies improve, and travelers begin interacting with people from many different lands? If each country is using a different prime meridian to mark 0 ° longitude, then it would be impossible to give someone from another country a location, and have them be able to accurately find it.

Over time, more and more travelers began to recognize the meridian passing through Greenwich, England, as the Prime Meridian. In 1884, a group of scientists, navigators, and businessmen made Greenwich, England, the official worldwide Prime Meridian.

The further away from the Prime Meridian that one travels the higher their longitude becomes, until they reach 180 ° longitude. If an individual is in the Eastern Hemisphere, their longitude is measured in degrees east. If they are in the Western Hemisphere, their longitude is measured in degrees west.

Plotting Your Location

Using longitude and latitude, it is now possible to accurately describe any location on the Earth within a correct distance of only a few inches. Your home or school probably has a street address. Perhaps it looks something like 6088 Garden Gate Drive. These numbers tell the mailman where to deliver your mail, and visitors how to find you. While physical addresses are very useful, longitude and latitude are more concise and accurate. A physical address is based on a local system, understood and accepted only by a small community. Longitude and latitude are accepted worldwide by the entirety of humanity. If you know your longitude and latitude, you can tell a distant pen pal exactly where you are on this sphere-shaped planet.

For hundreds of years, calculating your longitude and latitude was a somewhat difficult process. Using specialized tools and the stars as a guide, trained experts could determine their location, and make sure that their travels were still on course. However, due to the limits of their equipment, these measurements were only approximate.

Today, anyone can quickly and accurately measure their location on the Earth. One popular method for determining the latitude and longitude of an object is through the use of Global Positioning Satellites, or GPS. Inexpensive GPS devices use the signals from satellites orbiting the Earth to calculate the exact location of the person holding the device. Many of these devices also allow the user to save their favorite locations in a small computer so that these locations can quickly be found in the future.

Do you want to visit a hidden waterfall in the middle of the vast Utah desert? You could get directions from the locals, but chances are high that you will get lost. In the desert, everything looks pretty much the same. How do you know that you going in the right direction? Using GPS as your guide, you can rest assured that you are not going to get lost. Look up the exact longitude and latitude of the waterfall, either online or in a book. These coordinates can then be entered into the device, which can then be used to guide you to the exact spot where the waterfall is hidden. These advances in technology make traveling much easier today than it was in the past.