How to use the simulator
The one control is the transport cost t slider. It runs from 0.5× to 2.5× in steps of 0.1 and starts at 1.0×. It multiplies how fast every land use's rent falls with distance from the market.
- Ring map. Concentric rings around a central MARKET point: dairy/market gardening, forest, grain and ranching, from the inside out. The pale outer area is labelled "beyond margin: no cultivation".
- Legend. Each land use with its distance band in km and a short reason for its position, such as "perishable, intensive → pays the most, must be closest".
- Bid-rent graph. Rent against distance from the market (0–24 km) for all four uses. Thin lines show each use's bid, a heavy line traces the upper envelope (the winning bid at each distance), and dashed verticals mark the ring boundaries.
At the default 1.0×, the legend reads: dairy 0.0–5.0 km, forest 5.0–8.3 km, grain 8.3–14.4 km and ranching 14.4–22.9 km.
The map and graph only show the first 24 km. At low transport costs (about 0.6× and below) the farmed area reaches past that edge, and the ranching row in the legend shows as 24.0–24.0 km. That does not mean ranching has disappeared. Its ring has moved beyond the area drawn on screen.
The key ideas
Johann Heinrich von Thünen (1826) asked why farmland near a city is used differently from land farther out. He assumed an isolated state: one central market, flat land of equal fertility, no outside trade, farmers who maximize profit, and transport costs that rise in proportion to distance.
Each land use's bid rent is the most it can pay for land at a given distance and still break even. In the simulator each use's rent falls along a straight line:
- is the rent the use could pay at the market (higher for intensive, valuable products).
- is how quickly its transport costs mount with distance (steeper for perishable or bulky goods).
- is distance and is the transport cost setting.
Where two lines cross, the land changes hands, so the boundary between two uses is at . The rings in the model follow from this:
- Ring 1, dairy and market gardening: perishable produce, high value per hectare and the steepest bid-rent line.
- Ring 2, forest: wood for fuel and building was heavy and bulky, so it was too costly to haul far.
- Ring 3, grain: it keeps well and is relatively cheap to transport.
- Ring 4, ranching: extensive land use on cheap land, and the animals could walk to market.
Every boundary is divided by , so raising transport cost shrinks all the rings by the same factor. The order of the rings and their proportions stay the same, and the outer margin of cultivation moves in toward the market.
Worked example
Problem: Fuel prices double, so transport costs double from 1.0× to 2.0×. Predict the new ring boundaries.
Step 1: Start at 1.0×. The dairy–forest boundary comes from the simulator's two bid-rent lines: km. The other boundaries are 8.3 km and 14.4 km, and ranching ends at 22.9 km, where its rent reaches zero.
Step 2: Double t. Every boundary halves: , , and km.
Step 3: Check it in the simulator. Set t to 2.0×. The legend reads dairy 0.0–2.5 km, forest 2.5–4.2, grain 4.2–7.2 and ranching 7.2–11.4. All four rings are still there, each half as wide as before, and the land between 11.4 and 22.9 km falls outside the margin of cultivation.
Step 4: Interpret. Cheap transport does the opposite: it pushes farming outward and lets distant regions supply the city. Refrigerated trucks and container shipping have stretched the rings to a global scale.
Common mistakes on the AP exam
- Putting forest on the outside. In von Thünen's model forest is the second ring, because timber and firewood were heavy and needed every day.
- Explaining ring order by crop value alone. Position depends on the trade-off between value per hectare and transport cost, which is exactly what the slope of each bid-rent line represents.
- Forgetting the assumptions. If a question asks why a real region does not form rings, point to a specific assumption that fails: rivers or highways, varied soils and terrain, more than one market, or government subsidies.
- Mixing up rural and urban bid rent. Von Thünen's model is about agricultural land around a market town (Unit 5). Urban bid-rent theory, where offices outbid housing near the CBD, belongs in Unit 6.
- Saying the model is useless today. The model's logic still holds. Intensive market gardening and dairying still cluster near large cities, and the same rings appear at a global scale.
When the AP exam uses this
The von Thünen model is topic 5.8 in Unit 5 (Agriculture and Rural Land-Use Patterns and Processes). Expect a ring diagram to label, a question about why a given product sits in a given ring, or a free-response prompt asking you to apply the model to a real region and explain one way modern transport has changed it.