Vector graphic

Vector graphics describe an image as mathematics, points, lines, curves and fills, rather than as a fixed grid of coloured dots. A circle is stored as a centre, a radius and a colour, so the computer redraws it at whatever size is asked for. The consequence is the defining property of vector art: it scales to any size with no loss of sharpness.

Inside a PDF, most of what is not a photograph is vector: the text outlines, logos, line art, charts and diagrams are all drawn from path instructions in the page content stream. Zoom into a vector logo and the edges stay crisp at 100% or 1000%, because the renderer recomputes the curve at the new scale instead of stretching pixels. Vector content also tends to be compact, since a few coordinates can describe a shape that would take thousands of pixels to store as an image.

The trade-off is that vectors suit geometric, well-defined shapes, not the continuous tonal variation of a photo, which is the job of raster images. SVG is the common web vector format, and PDF's own drawing model is vector at its core.