Vectors vs rasters

See image format article for some advantages and disadvantages of various image formats. What does 'image' mean? It's a 'raster' or 'bitmap'. That is, a discretized (pixel-based) grid of data.

What are vector graphics?
What I was not writing about was drawings and graphics combining text, lines, and images. Such files usually contain vector graphics. Vector graphics do not contain descriptions of pixels, but instead they contain descriptions and positions of text, paths, and polygons. Example file formats are:


 * SVG — Scalable Vector Graphics, an open format and web standard
 * AI — a proprietary format used by Adobe Illustrator
 * CDR — CorelDRAW's proprietary format
 * PPT — pictures in Microsoft PowerPoint are vector format
 * SHP — shapefiles are a (mostly) generic vector format for GIS

One of the most important properties of vector graphics is that you can rescale it without worrying about changing the resolution.

What are composite formats?
Vector and raster graphics can be combined in all sorts of ways, and vector files can contain raster images. They can therefore be used for very large displays like posters. But vector files are subject to interpretation by different software, may be proprietary, and have complex features like guides and layers that you may not want to expose to someone else. So when you publish or share your work it's often a good idea to export to either a high-res PNG, or a composite page description format:


 * PDF — Portable Document Format, the closest thing to an open, ubiquitous format; stable and predictable.
 * EPS — Encapsulated PostScript; the precursor to PDF, it's rarely called for today, unless PDF is giving you problems.
 * PS — PostScript is a programming and page description language underlying EPS and PDF; avoid it.
 * CGM — Computer Graphics Metafiles are best left alone. If you are stuck with them, complain loudly.
 * WMF or EMF — Windows Metafile, and Enhanced Windows Metafile. Just say no.

There's one situation when you should favour a composite format over anything else: when you are sending something for printing. Some image formats do support the CMYK colour space, but it's not normal, and not easy. So if you need CMYK and very high resolution (use 300 dpi or more for print), then stick to PDF for output. In fact you're going to save yourself a lot of trouble if you just stick to Adobe for as much of your cycle as you can afford.

What software do I need?
Any time you want to add text, or annotation, or anything else to a raster, or you wish to create a drawing from scratch, vector formats are the way to go. There are several tools for creating such graphics:


 * Adobe Illustrator — the top banana (no longer that expensive; check out Adobe Creative Cloud)
 * Inkscape — free and open source (our favourite)
 * ACD Canvas
 * CorelDRAW

Judging by figures I see submitted to journals, some people use Microsoft PowerPoint for creating vector graphics. For a simple figure, this may be fine, but for anything complex — curved or wavy lines, complicated filled objects, image effects, pattern fills — it is hard work. And the drawing tools listed above have some great advantages over PowerPoint — layers, tracing, guides, proper typography, and a hundred other things.

Plus, and perhaps I'm just being a snob here, figures created in PowerPoint make it look like you just don't care. Do yourself a favour: take half a day to teach yourself to use Inkscape, and make beautiful figures for the rest of your career.