In 1826 a German landowner, Johann Heinrich von Thünen, asked a simple question: if every acre were the same, what would farmers grow at each distance from the market? His answer, in The Isolated State, explains the farming patterns around cities in his day and shows how geographers use models.
Key idea
Imagine one market town on a flat, uniform plain, with no roads and the same soil everywhere. Because carrying goods costs more the farther they go, farm uses form rings: market gardening and dairy closest, then forest (wood for fuel and building), then grains and field crops, and ranching farthest out.
Why it works
Each farmer earns what is left after paying to grow the crop and to haul it: a profit, or land rent, per hectare. Near town every use is profitable, so land goes to the use that earns the most there: perishable, heavy or bulky goods such as milk, vegetables and firewood, which cost a lot to haul. Farther out, those costs eat their profit, and uses that are cheap to move per hectare, such as grain and animals that walk to market, win instead.
The idea can be written as a formula, with yield $Y$ (tons per hectare), price $p$ and growing cost $c$ (per ton), freight rate $f$ (per ton per km) and distance $d$ (km):
$$\text{rent per hectare} = Y(p - c) - Y f d$$
Worked example: Rent at a distance
Wheat yields 3 tons per hectare, sells for 200 and costs 120 per ton to grow, and hauling costs 1 per ton per km. What is the rent per hectare at 30 km?
- Profit before hauling: $3 \times (200 - 120) = 240$.
- Hauling: $3 \times 1 \times 30 = 90$.
- Rent: $240 - 90 = 150$.
Answer: 150 per hectare.
Worked example: Where the ring ends
For the same wheat, how far from market does the rent fall to zero?
- Set $Y(p - c) = Y f d$, so $d = (p - c) / f$.
- $d = (200 - 120) / 1 = 80$ km.
- Beyond 80 km, growing wheat for this market loses money.
Answer: 80 km.
Common mistake
Thinking the rings come from soil. In the model the land is the same everywhere; the rings come from the cost of carrying goods to market. Real maps add rivers, roads, refrigeration and different soils, which stretch and break the rings, but the logic of transport cost still shows up.
Von Thünen put forest in the second ring because wood for fuel and building was heavy and needed in large amounts. That ring has faded from modern maps since coal, oil and trucks changed the costs, a reminder that a model fits the conditions it was built for.