Directions
16. Directions may be referred either to the Horizontal or to the Vertical. Referring them to the horizontal, we say of a certain direction, that it is up-to-the-left, or up-to-the-right, or down-to-the-left, or down-to-the-right, a certain number of degrees. It may be thirty (30°), it may be forty-five (45°), it may be sixty (60°),—any number of degrees up to ninety (90°), in which case we say simply that the direction is up or down. Directions on the horizontal may be described by the terms, to the right or to the left.
The method of describing and defining different directions from any point, as a center, is clearly explained by this diagram.