The elementary concept of Area becomes much more useful later, both in applied mathematics, mensuration and geometry, and in high school topics like integral calculus, where we find the area under a curve.
Similarly, the length of the boundary of a shape, or the Perimeter or Circumference, are important concepts. At more advanced levels the Perimeter is used in the Distance Formula and in the length of a curve between two points (which also uses calculus, like the area under a curve).
This book contains every formula that a high school student or someone looking to brush up on geometry and mensuration concepts will need.