A histogram is a graph where a set of rectangles are represented as per the class intervals and the frequencies. The class intervals are marked on the X-axis and frequencies on Y-axis. The scales for both the axes are the same. A rectangle is drawn considering class intervals as base and frequencies as height. If the intervals are equal then the area of the rectangle is directly proportional to frequency. So in a histogram, if the area of the rectangle is proportional to its frequency, we can say that the lengths of the rectangles are also proportional to the frequencies.