This is where pictures can be described by numbers.
To do this we use a two dimensional space called the 'number plane'. This is an extension of the number line into two dimensions: left/right (the 'x' axis) and up/down (the 'y' axis)
To specify a 'point' on this number plane we use a pair of numbers like this: (3,5), where the first number '3' is how far left/right it is, and the second number '5' is how far up/down it is. The point (3,5) would be in the top right hand side of the number plane 3 across and 5 up.By putting multiple points on we can build up lines, and then we can make any shape or picture that we want. So we could draw a black and white Mona Lisa simply be specifying a whole series of points.
This system was worked out by a French dude name Renee Descartes about 400 years ago, and is also known as the 'Cartesian' coordinate system. Most computer games use this system to calculate and display objects on the screen.
