There are points, lines and planes.

• Any plane is a 2 dimensional space as already discussed.
• Three points not on a line determine a plane containing all three;
  • A point and a disjoint line determines a unique plane containing both;
  • A point and a direction or line determines a unique plane normal to the line through the point.
• 2 lines either lie in a single plane or are skew (not both).

Points can be considered as abstract objects. To conveniently represent their properties we usually introduce some additional structure. In particular we describe points and lines and planes by using vectors, and obtain numerical representations of the vectors by introducing an origin and a set of basis vectors.