FIGURE 3 DEMAND FOR PUBLIC GOODS: VERTICAL SUMMATION OF INDIVIDUAL DEMAND CURVES
For public goods, exclusion is not possible, individuals can consume the good simultaneously, and market demand is found by summing vertically. Market demand for public goods is really a willingness-to-pay curve because the government will have to provide the good and levy taxes to pay the cost. The total demand for the public good is shown by the heavy line labeled DPublic Goods and is the vertical summation of individual demands.