Two numbers, one place
How Do You Describe Exactly One Square?
Coordinates name a point by saying how far across and how far up it sits.
-
Step 1 of 5
Describing a spot in words is hopeless.
Near the middle, a bit to the left of that tree. Everyone pictures somewhere different, and nothing can be checked or repeated.
-
Step 2 of 5
A grid gives every square a name.
Lay lines across and up, and each crossing becomes a place that can be pointed to by counting from an agreed starting corner.
-
Step 3 of 5
The order of the two numbers is fixed.
Across always comes before up. Swap them and you land somewhere completely different, which is why the convention matters so much.
-
Step 4 of 5
Everything is measured from one agreed corner.
The origin is where both counts start at zero. Without a shared starting point the two numbers would mean nothing to anybody else.
-
Step 5 of 5
The same idea runs maps and screens.
Grid references, latitude and longitude, and the position of every pixel on this screen are all the same two-number trick.
Screen coordinates usually count downward from the top-left corner, the opposite of the maths convention, which trips up new programmers.
The short version
Coordinates name one exact place with two numbers in an agreed order, measured from a shared starting corner.
Try it yourself
Play battleships. The whole game runs on naming one square with a letter and a number in a fixed order.
Topics