Coordinates (a, b) of a point in a rectangular coordinate system, where abscissa A represents the horizontal position of the point and ordinate B represents the vertical height of the point. For example, the point (3, -2) can be drawn by translating three units to the right from the origin and then translating three units downward, and the obtained position is the position corresponding to the point (3, -2).

The coordinates (r, θ) of the point in the polar coordinate system, where r represents the distance from the point to the origin, and θ represents the counterclockwise rotation angle from the positive and semi-axis of the X axis. For example, the point (2, π/3) can be drawn as follows: first, make a circle with the origin as the center and 2 as the radius, and then start from the intersection of the positive semi-axis of the X axis and this circle and rotate it counterclockwise by 60 degrees to get the position corresponding to the point (2, π/3).

Points on a plane can be represented by rectangular coordinate planes or polar coordinate planes.

In a sense, rectangular coordinate plane can be understood as "square" and polar coordinate plane can be understood as "circle". (Of course, it can extend to all directions infinitely. )