Constructing a Graph: Axes, Origin and Scale

Every graph in this chapter is built on the same skeleton: two straight reference lines drawn perpendicular to each other.

• The horizontal line is the X-axis; the vertical line is the Y-axis.
• Their point of intersection is the origin, written (0, 0) — both variables equal zero here.
• Moving right along the X-axis and up along the Y-axis represents positive values; moving left or down represents negative values (though most economic diagrams, dealing with prices and quantities, stay in the positive quadrant only).
• The scale is the value that one unit of distance on an axis represents (for example, "1 cm = 10 units"). The X-axis and Y-axis may use different scales from each other. …