ELI5 Longitude and Latitude


I don’t understand these two

In: Physics


Think of the claw game at the arcade. You can only move left-right, or front to back. You can’t move diagonal. To win a piece, you have to move exactly so many inches on the left-right line, then the front-back line. The left right and front back lines are latitude and longitude, and the EXACT spot to drop the claw, down to a very specific number, is how coordinates for a given location works.

[This image might help you](https://upload.wikimedia.org/wikipedia/commons/b/bc/FedStats_Lat_long.png). Latitude and longitude are coordinates that tell you where on the surface of the Earth you are. Latitude is how far north or south of the equator you are. Lines of latitude run parallel to the equator going to the the poles. Longitude is how far east or west you are from the prime meridian. Lines of longitude run perpendicular to the equator towards the poles.

If you have a flat plane, like a sheet of paper, it’s pretty easy to assign coordinates to it in such a way that you can easily designate any point on that plane. Think of your typical graph in mathematics (x-axis and y-axis) and you’ve got the right idea. But the Earth is not a flat plane, so assigning coordinates on it is a bit trickier. There’s no corner to start from, and if you go far enough in one direction you wrap back around to where you started. Latitude and longitude are a *coordinate system*: a way to use numbers to define where you are on the surface of the globe.

Let’s start with latitude. You need to pick a starting point; and, as previously noted, there isn’t a convenient one like a corner. So the starting part is the Equator, the Earth’s widest point. You draw a line all the way around that widest point and call that zero. You then draw similar lines at even intervals all the way up and now you have a scale that can tell you how far something is from your zero point. Anything north of the zero point has a positive value on the scale and anything south of the zero point has a negative value. That’s basically what latitude is: a number that tells you how far something is away from the Equator in a north/south direction.

That alone isn’t enough to tell you where something is though. If you know that something’s at 30 degrees north latitude, there’s a whole band of places that could be (basically any spot along that band). Describing a point on that band is a bit tricky. You can’t just use distance because the total size of the band changes depending on how far away it is from the equator. You need to use something where any given value of it exists exactly one time on each band of latitude; so you define *meridians*, which are lines that stretch from the North Pole, curve around the Equator, and reach the South Pole. You draw these all around the globe to that they’re evenly spaced at any given band of latitude (although they’ll be differently spaced at different latitudes). You pick one of these to be the zero point (the Prime Meridian, which passed through Greenwich in England) and then you can count how many meridians something is from the zero point.

Now you have a coordinate system that allows you to locate anything on Earth by describing essentially how far it is from the equator (latitude) and how far it is from the Prime Meridian (longitude) in a way that doesn’t fall apart on a curved surface.