Why A Smith chart is a graphical plot of normalized complex impedance, Z = R + jX. The full circles printed on it are lines of constant resistance, and the arcs that curve off the horizontal axis are lines of constant reactance (positive/inductive above the centerline, negative/capacitive below). Reading where a resistance circle crosses a reactance arc gives you the impedance at that point on a line.
Watch out Inductance and capacitance is tempting because the upper and lower halves of the chart are inductive and capacitive, but the chart is scaled in ohms of reactance, not in henries or farads, and inductance/capacitance ignores the resistance family entirely.
Smith chart = R circles + X arcs, because it plots Z = R + jX.