One economic rule, four applications
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1 · Households
Higher commuting cost creates a steeper bid curve and a stronger incentive to locate near the CBD.
2 · City system
A transport improvement changes central rent in a closed city but population and the boundary in an open city.
3 · Production
Revenue net of nonland cost sets the intercept; freight cost sets the slope.
4 · Development
The landowner chooses the building that supports the highest bid per hectare at that location.
1. A linear city with two household types
Walkers face a larger opportunity cost per mile than drivers. Competitive bidding sorts the steeper curve closer to the CBD and joins the two curves into one equilibrium envelope.
City-size assumptions
The number of each household type determines how much of the city it occupies. Bid curves meet at the sorting boundary so households remain indifferent at the margin.
2. Closed city versus open city
When travel becomes faster, a closed city keeps its households and boundary fixed. An open city instead holds the CBD bid at the outside-market level and adjusts through migration.
In the open-city comparison, the initial CBD bid is the utility-equivalent rent available in the wider system. Migration expands or contracts the city until that bid is restored.
3. Competing producers and the land-rent envelope
Under zero economic profit, each producer can pay its revenue minus nonland and transportation costs. The activity offering more at a location wins the land.
A steeper curve does not necessarily imply a larger bid everywhere. Land use changes where the two offers intersect; beyond the zero-bid point, that activity cannot profitably occupy land.
4. Which building should be built?
All three designs provide one hectare of office space. A taller building uses less land but costs more capital. The winning design is the one that supports the highest bid rent per hectare.
Building design assumptions
| Design | Lot ha | Floors | Capital | Total land bid | Bid/ha |
|---|
The tall design capitalizes scarce central land through more floors. Farther out, lower-density designs can win because saving capital matters more than saving land.
Three ideas to retain
Access is capitalized
A larger cost of distance produces a steeper bid-rent gradient because central locations save more travel resources.
The envelope is the market
Individual curves describe willingness to pay. The highest feasible bid at each location determines rent and land use.
Equilibrium depends on closure
Fixing population versus allowing migration changes which outcome—rent, population, or the city boundary—absorbs a shock.