Icons are widely used in infographics such as maps and pictographs. So as a visualization designer, you’ll get to the point where you must choose which icons or pictograms to use. But please, choose wisely.
The reason I got to this topic is a recent post by Naomi Robbins about two opinions on the usefulness of pictographs. She reminded my of a critical article by Stephen Few, who stated that unit charts (another term for pictographs) are for kids, but not for serious information displays. My biggest complaint about his article is that he picked some of the worst imaginable examples to back up his arguments.