**Zone**

A *zone* is that portion of the surface of the sphere included between two parallel planes.

**Properties of Spherical Zone**

- The
*bases*of the zone are the circumference of the sections made by the two parallel planes. - The
*altitude*of the zone is the perpendicular distance between these two parallel planes. - If one of the bounding parallel planes is tangent to the sphere, the surface bounded is a
*zone of one base*.

**Area of the Zone**

The area of any zone (one base or two bases) is equal to the product of its altitude h and the circumference of the great circle of the sphere.

$A_{zone} = \text{circumference of great circle } \times \text{ altitude}$

$A_{zone} = 2\pi Rh$

Note that when h = 2R, the area of the zone will equal to the total surface area of the sphere which is 4πR^{2}.