Select any visualisation/infographic and looking at any individual chart included. Try to extract and write down in language terms what this chart shows across the angle, the framing, and (where relevant) the focus?
Does it feel that the definition you have arrived at is consistent with the aims/claims of the chart as it is published? In other words does the chart show and include what you think it is actually supposed to be doing or is there a disconnect?
Assignment Link: http://book.visualisingdata.com/chapter/chapter-5