The Cartesian (Rectangular) Coordinate System
We all know that locations such as mile markers on the highway or places on maps or street addresses may be specified by numbers. We locate points on a number line by assigning a number to each point on the line. One point is arbitrarily labeled with a 0 and another point with a 1. All other points are labeled accordingly as shown on the line below, using equal spacing between every pair of consecutive whole numbers:
Generally, on a horizontal number line, the positive numbers are to the right of zero and the negative numbers are to the left of zero.
On a vertical number line, the positive numbers are above zero and the negative numbers are below zero as shown above.