JPEG (Joint Photographic Experts Group)

JPEG is the most widespread raster format: every program, every phone and every browser opens it, and lossy compression keeps the file small. For a map it is a finished picture — drop it into a presentation, send it in a messenger, put it on a web page.

The choice between JPEG and PNG is simple. If the map has many flat fills, thin lines and labels, PNG will be cleaner: it compresses losslessly. JPEG wins on weight and suits cases where the picture goes to the web, into email or into a document and file size matters.

The map is rendered into an image and saved at quality 90 out of a hundred — the balance at which compression artifacts are invisible to the eye. Quality is adjustable from 60 to 100, the default resolution is 150 dots per inch, and the sheet is A4 in landscape orientation.

There are technical ceilings: no more than 50 million pixels per image and no more than 10,000 pixels on any side. Transparency does not exist in JPEG at all — empty places are filled with a solid color; if you need a transparent underlay, take PNG.