The assumptions are: (i) all dwellings must contain exactly 1,500 square feet of fl oor space, regardless of location, and (ii) apartment complexes must contain exactly 15,000 square feet of fl oor space per square block of land area. These land-use restrictions, which are imposed by a zoning authority, mean that dwelling sizes and building heights do not vary with distance to the central business district, as in the model from chapter 2. Distance is measured in blocks. Exercises 251 Suppose that income per household equals $25,000 per year. It is convenient to measure money amounts in thousands of dollars, so this means that y = 25, where y is income. Next suppose that the commuting cost parameter t equals 0.01. This means that a person living ten blocks from the CBD will spend 0.01 10 = 0.1 per year (in other words, $100) getting to work. The consumer ' s budget constraint is c + pq = y - tx , which reduces to c + 1,500 p = 25 - 0.01 x under the above assumptions. Since housing consumption is fi xed at 1,500, the only way that utilities can be equal for all urban residents is for bread consumption c to be the same at all locations. The consumption bundle (the bread, housing combination) will then be the same at all locations, yielding equal utilities. For c to be constant across locations, the price per square foot of housing must vary with x in a way that allows the consumer to afford a fi xed amount of bread after paying his rent and his commuting cost. Let c * denote this constant level of bread consumption for each urban resident. For the moment, c * is taken as given. We ' ll see below, however, that c * must take on just the right value or else the city will not be in equilibrium. (a) Substituting c * in place of c in the budget constraint c + 1,500 p = 25 - 0.01 x , solve for p in terms of c * and x . The solution tells what the price per square foot must be at a given location in order for the household to be able to afford exactly c * worth of bread. How does p vary with location? Recall that the zoning law says that each developed block must contain 15,000 square feet of fl oor space. Suppose that annualized cost of the building materials needed to construct this much housing is 90 (that is, $90,000). (b) Profi t per square block for the housing developer is equal to 15,000 p - 90 - r , where r is land rent per square block. In equilibrium, land rent adjusts so that this profi t is identically zero. Set profi t equal to zero, and solve for land rent in terms of p . Then substitute your p solution from (a) in the resulting equation. The result gives land rent r as a function of x and c*. How does land rent vary with location? Since each square block contains 15,000 square feet of housing and each apartment has 1,500 square feet, each square block of the city has 10 households living on it. As a result, a city with a radius of x blocks can accommodate 10 2 x households ( x2 is the area of the city in square blocks). 252 Exercises (c) Suppose the city has a population of 200,000 households. How big must its radius x be in order to fi t this population? Use a calculator and round off to the nearest block. (d) In order for the city to be in equilibrium, housing developers must bid away enough land from farmers to house the population. Suppose that c * = 15.5, which means that each household in the city consumes $15,500 worth of bread. Suppose also that farmers offer a yearly rent of $2,000 per square block of land, so that rA = 2. Substitute c * = 15.5 into the land rent function from (b), and compute the implied boundary of the city. Using your answer to (c), decide whether the city is big enough to house its population. If not, adjust c * until you fi nd a value that leads the city to have just the right radius. (e) Using the equilibrium c * from (d) and the results of (a) and (b), write down the equation for the equilibrium land rent function. What is the rent per square block at the CBD ( x = 0) and at the edge of the city? Plot the land rent function. How much does a household living at the edge of the city spend on commuting? (f) Suppose that the population of the city grows to 255,000. Repeat (c), (d), and (e) for this case (but don ' t repeat the calculation involving c * = 15.5). Explain your fi ndings. How does population growth affect the utility level of people in the city? The answer comes from looking at the change in c * (since housing consumption is fi xed at 1,500 square feet, the utility change can be inferred by simply looking at the change in bread consumption). Note that because they are fi xed, housing consumption doesn ' t fall and building heights don ' t rise as population increases, as happened in the model in chapter 2. Are the effects on r and x the same? (g) Now suppose that population is back at 200,000 (as in (c)) but that rA rises to 3 (that is, farmers now offer $3,000 rent per square block). Note that, unlike in the lectures, the x value can ' t change as rA rises (what is the reason?). Repeat (d), (e) for this case. Compare your answers with those in (f). (h) Now suppose that instead of being located on a fl at featureless plain, the CBD is located on the ocean (where the coast is perfectly straight). This means that only a half-circle of land around the CBD is available for housing. How large must be the radius of this half-circle be to fi t the population of 200,000 residents? Using your answer, repeat (d) and (e), assuming that all parameters are back at their original Exercises 253 values. Are people in this coastal city better or worse off than people in the inland city of (c) and (d)? (Assume unrealistically that people don ' t value the beach!) Can you give an intuitive explanation for your answer? (i) Finally, focus again on the inland city, and suppose that the zoning authority imposes a building height restriction. This restriction limits housing square footage per block to 7,500, half the previous amount. The cost of building materials per square block falls from 90 to 43 (note that the cost is less than half as much because of diminishing returns). Find the new value of x (compare the answer in (h)), and repeat (d) and (e). How does the height restriction affect the utility of urban residents? Explain intuitively why this effect emerge. Does the restriction seem to be a good policy?