It is common in the IELTS Writing paper to be asked to describe a bar graph. Bar graphs, also known as bar charts, are similar to line graphs in that they have two axes and are useful for showing how something has changed over a given period of time, especially when there are significant changes. Bar graphs consist of rectangular bars, which can be orientated horizontally or vertically, with the lengths proportional to the data values that they represent. They are typically used for comparing two or more values.