Pictographs are as simple as a statistical graph can get. Pictographs are good for schoolchildren learning about graphing, but they are to simple to be used for more advanced data. Older students will rarely be able to use pictographs for graphing more complex sets of data.
Pictographs rely on pictures to represent data. One picture equals a set amount of units. But these graphs become difficult to use once non-whole numbers are used. Even if a key is used for half and quarter numbers, it is almost impossible to represent exact numbers. This makes pictographs unreliable for anything other than whole and half numbers.
Pictographs' icons resemble assigned amounts. For example, if the icon is a dollar sign for a fund-raiser, one sign might equal $50. Because the numbers represented in the graph are approximate, amounts can be misrepresented, and this can sway viewers' opinions of the data in the pictograph.
Icon size can mean various things. Some graphers use a bigger icon to represent a larger amount of data. However, it can be confusing if larger icons are used with no variation in data. If graphers want to use larger icons to represent larger numerical amounts, the whole picture should be bigger instead of taller or longer.