When we have different classes of data, there is always an upper and a lower class limit for it i.e. the dataset has a smallest and largest value. Class boundary is the midpoint of the upper class limit of one class and the lower class limit of the subsequent class. Each class thus has an upper and a lower class boundary. It must be noted that upper class boundary of one class and the lower class boundary of the subsequent class are the same. Class boundaries are not a part of the dataset.