Vector files.

What is a vector file?

Vector images don’t use pixels. They’re created with numerical expressions that define shapes, lines, and curves using positions (coordinates) on a grid. Because the grid can be any physical size (think of the street map of your city shown on your smartphone screen, on the page of a guidebook, or printed on a wall), the shapes can be made larger or smaller by changing the size of the grid or the numbers that define the points. Internally, a vector file is really a list of instructions that tell a computer program where to place points on a grid, how to join them up, and what colors they should be.

When you see an image or illustration that comes from a vector file, it has been translated into pixels on a screen or pigment dots on a substrate such as paper: it has been “rasterized.” A raster is a mosaic of tiny shapes, usually square. You commonly see it expressed as a number of horizontal and vertical pixels (“1920 by 1080 pixels” is the raster on a “Full HD” screen), often called the “resolution” of the output. There is a fixed number of dots in a raster, so the only way you can make one bigger or smaller is by changing the size of the dots or the distance between them. This is why a tiny photograph looks pixelated when you enlarge it too much.

The important thing to keep in mind is that the word “resolution” applies only to the raster representation of the information in a vector file. If your vector drawing is a perfect rectangle, its output will always be a perfect rectangle, whether it is on a postage stamp or the side of a building. It never gets pixelated because it didn’t have any pixels to begin with, only drawing instructions.

Advantages and disadvantages of vector files.

There are both pros and cons to using vector images over the raster format.