The PointInPolygon function determines whether a given point in the plane lies inside or outside of a polygon. It has various applications in many fields such as computer graphics, geographical information systems (GIS), and CAD.
In the following example, point A is in the polygon and point B is outside of the polygon.
A use case for this function is to determine in which "drive-time polygon" surrounding a store a customer resides. This information helps in mailer targeting.
Another use case is to determine which cell phones are frequently within a polygon surrounding an airport. This information helps in identifying frequent fliers.