system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a "vector" image?

I often get confused when people at my work place ask for "vector". Starting design myself, it gets confusing because people do not know the meaning of what vector really is or at least I get confused from .ai, .psd files and so on.

So how can I explain what vector really is? And is it only limited to adobe programs?
gpt
There are two general kinds of computer graphics: *raster* graphics and *vector* graphics.

Imagine a big piece of graph paper.

A raster image says how each *square* on the paper should be colored — as in, "square 3,2 is blue ... 3,3 is purple ... 3,4 is purple too ... 3,5 is black ..." and so on. Everything in a raster image is in terms of pixels, which are the squares on the graph paper; each pixel is given a color.

A vector image is, instead, instructions for how to draw lines and shapes among the *intersections* on the paper — as in, "draw a triangle from 1,2 to 4,5 to 0,3 and fill it with purple." A vector image does not talk about individual pixels at all; only about shapes (lines, triangles, circles, and so on) and which coordinates they are placed.

One big difference is that vector images scale smoothly whereas raster images do not. If you want to make a vector image 2x bigger, you just multiply all the coordinates by two. If you want to make a raster image 2x bigger, you have to average all the colors of the pixels to make the in-between pixels. This makes it fuzzier, whereas a vector image stays sharp.