A continuous category, such as age, may have a large number of possible values and this could result in complex histogram with so many columns that it becomes difficult to interpret the information. For this reason the data in a histogram are often grouped to reduce the number of categories. For example, instead of drawing a bar for each individual age from 16 onwards, the data in the histogram below have been grouped into a series of continuous age ranges: 16-24, 25-34 etc.