For example, if we shop the floor in our home, as long as the floor we buy is as big as the indoor floor, regardless of the floor size; You can just cover it with ground. If we don't know the concept of area, we can't know how many land plates can cover the ground. For another example, if we want to make a bigger quilt, we must buy fabric splicing, because the width we need is not that big; How much cloth do you need? Let's calculate the area.