The Earth’s coordinate system

Understanding climate data requires familiarity with how our planet is geographically mapped. So, if we visualize the Earth as a sphere, we can pinpoint any location in a universally accepted way using a system of coordinates.

Meridians and longitude

We can draw lines vertically from the North Pole to the South Pole at regular intervals. These lines are called meridians. Each meridian has an associated constant value known as longitude, which is measured in degrees.
By convention, the Prime Meridian runs through the Royal Observatory in Greenwich, United Kingdom and has longitude set at 0°.
Longitude values decrease westward up to -180° and increase eastward up to 180°.

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Parallels and latitude

Now that we’ve established a universal method for determining the east-west position on Earth, let’s explore how we define positions from north to south.
Now we have to imagine drawing a line around the Earth that is equidistant from both poles, stretching from east to west. This line is called the Equator. Lines running parallel to the Equator are known as parallels.
The position of these parallels is determined by their angle relative to the horizontal plane passing through the Equator. This angle is referred to as latitude, which is also measured in degrees. Latitude values increase from the Equator northward up to 90° and decrease southward down to -90°.

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This system allows us to specify any location on Earth using a universally understood method.

In the analyses we will conduct, we will sometimes want to isolate areas, regions, or even continents, and to do this we will specifically use latitude and longitude to filter data relevant only to the areas of interest.

However, when dealing with climate data, it’s crucial to remember that climate is related not only to the Earth surface, but also to atmospheric conditions. Therefore, to gain a comprehensive understanding of our planet’s climate, we must consider a more complex representation. We will explore this further in the next chapter.