Geography as constraint

Read a map for what it lets a state afford to want.

In 1776 Adam Smith pointed out that a wagon with two men and eight horses took six weeks to carry four tons from London to Edinburgh, while a ship with six men carried two hundred tons over the same period. That is a factor of roughly fifty, and almost everything about where cities are and which countries got rich first follows from it.

One number does most of the work

Geography is a vague word, so reduce it to what it costs to move a ton of something one kilometre. Water is about thirty times cheaper than a pre-industrial road. Rail and trucks narrowed the gap and did not close it.

A cargo can travel until the freight bill eats the margin, which gives one line:

reach = (value per ton × margin) ÷ cost per ton-km

And the territory a place can serve goes as the squareof that reach. Thirty times the distance is nine hundred times the market, which is the part nobody's intuition supplies.

Move a ton of

Heavy, cheap, and the thing a pre-industrial city needs most of. It sets where cities can exist.

900x

more territory the coastal city can serve, for the same cargo in the same year

Inland, a ton of grain reaches 58 km before the freight bill eats the margin. That is a hinterland, not a market. You can feed a town and you cannot feed a city, and you cannot specialize in anything.

Sea2,000 km
Navigable river875 km
Canal583 km
Rail250 km
Truck146 km
Pre-industrial road58 km
Air19 km

How far a ton gets before freight eats a 35% margin. Rail and trucks compressed the ratio and did not remove it, which is why coastlines still decide things.

Switch the cargo and watch the map stop mattering. That is the other half of this lesson: geography is a constraint on cheap heavy things and almost nothing to a cargo worth three million a ton.

Worked example

Why a city has to be on water

Grain at 200 a ton, with a trader willing to spend 35% of it on freight.

By sea: about 1,750km. Which is roughly Alexandria to Rome, a grain trade that fed a city of a million people for three centuries.
By cart: about 58km. The same grain, the same year. A day and a half of walking, and then the horses have eaten the profit.
The ratio is 30, and the territory ratio is 900. A coastal city draws food from nine hundred times the area an inland one can.

That is not an advantage in trade. It is a different maximum population, and it is why the map of large pre-industrial cities is a map of coastlines and navigable rivers with very few exceptions.

Now switch the cargo to cloth at 6,000 a ton. It reaches 1,750km by cart, which is the same distance grain manages by sea. Same road, same carts, same century. This is why the Silk Road carried silk and not wheat: not because anybody preferred it, but because wheat could not pay the fare.

The London to Edinburgh comparison is in The Wealth of Nations, Book I, Chapter 3, which is out of copyright and free to read. Diocletian's Price Edict of 301 implies a land-to-sea cost ratio of a similar order. The model on this page is unit tested and calibrated so its distances reproduce journeys that actually happened rather than being chosen to look good.

ConventionEconomists call this value density: worth per unit of weight. It decides which transport a good can afford and therefore how far it travels, and it explains a lot of industrial location without any other input. Cement plants sit next to their customers. Watch factories sit wherever the watchmakers are. Nobody chose either arrangement, and the ratio of value to weight did.

What a map actually tells you

Navigable rivers, not rivers. A river you cannot move a barge up is scenery. What matters is depth, gradient, and whether it freezes. The United States has more navigable inland waterway than most of the rest of the world combined, and that fact does more work than any account of its founding.
Coastline you can use. Length is nearly irrelevant and natural deep-water harbors are not. A long straight coast with no shelter is a wall rather than a door.
Whether the borders are cheap to defend. Mountains, deserts, and water are cheap. An open plain is expensive, permanently, and the money comes out of whatever else the state wanted to do.
Who owns the exit.A landlocked country ships through somebody else's territory, which turns a transport question into a diplomatic one and puts a permanent third party in every trade.

What breaks

Geography constrains and does not decide. It sets what is cheap and what is expensive, and states with bad maps have done well and states with good ones have done badly. Anybody using geography to explain an outcome after the fact can explain any outcome, which is the tell that the explanation is not doing work.

The constraints move. Rail rewrote the interior of every continent. Containerization halved the cost of a sea leg. Refrigeration made distance survivable for food. A geographic fact is a fact about a technology as much as about the land, and the technology keeps changing.

Resources are the weakest part of the story. What is under the ground matters far less than whether you can move it and whether anybody can take it from you. That is the chokepoints lesson and the institutions lesson, and geography hands off to both of them rather than standing on its own.

What to do with this

When a country comes up, look for the water before anything else. Navigable rivers, usable harbors, and whether the exit belongs to somebody else. Those three tell you more about what the place can afford than its resources or its politics, and they were settled long before anybody currently alive had an opinion.

Then ask what the value per ton of its exports is, because that is the number that decides whether the map still binds. A country exporting ore is living in Adam Smith's world. A country exporting software is not, and the difference between them is not effort.

Test yourself

01Why did almost every pre-industrial city of any size sit on a coast, a navigable river, or a lake?

Because a city has to be fed, grain is heavy and cheap, and grain by cart runs out of margin in under sixty kilometres. A city off the water can draw on the fields it can see and no further, which caps it at a few tens of thousands of people.

Put the same city on a river and grain reaches it from eight hundred kilometres away. That is not a modest improvement in trade. It is a different quantity of available food, and therefore a different maximum size.

02A landlocked country and a coastal one have identical everything else. Estimate the disadvantage and say where it shows up.

Large, and it shows up as a permanent tax on every heavy thing the country makes or buys. The freight premium falls hardest on exactly the goods a developing economy starts with: agriculture, minerals, cement, basic manufacturing. All of those are low value per ton.

So the landlocked country is pushed toward things with a high value per ton, which are usually the things requiring skills and institutions it does not have yet. The disadvantage is not that trade is dearer. It is that the ladder's bottom rungs are missing.

03Has containerization made geography irrelevant?

It compressed the ratio and did not remove it. Sea freight is still roughly an order of magnitude cheaper per ton-kilometre than trucking, which is why factories cluster near ports and why the landlocked premium is still measurable. What did change is which goods care: anything with a high enough value per ton stopped noticing the map, which is why a chip fabrication plant can be almost anywhere and a cement works cannot.

A tutor that knows this lesson. It asks before it explains, and it will not tell you what to do with your own money.

Educational material, not investment or policy advice. Figures are cited where they come from a filing or a statistical series, and labelled as illustrative where they do not.