How is area defined for a flat shape?

Area is defined as the size of the surface of a flat shape. It quantifies the amount of space that a shape occupies within a given boundary. When calculating area, the focus is on measuring how much two-dimensional space is contained within the edges of the shape, typically expressed in square units (like square inches, square feet, etc.).

For example, for a rectangle, the area is calculated by multiplying its length by its width. This means the area gives a direct measure of how much of a flat surface is covered by the shape.

In contrast, perimeter refers to the total distance around the shape and does not account for the space within it, while the diagonal length describes a specific line segment that connects opposite corners of the shape without addressing the area itself. Thus, the correct definition clearly highlights that area pertains to the surface size rather than the edges or dimensions of the shape.