Unit 18 · Human Geography

In November of 2022 the United Nations announced that the world’s population had passed eight billion. That number is hard to picture, so start with a map. Shade every square where people live and most of the planet stays blank. Antarctica has no permanent residents. The Sahara, central Australia, Siberia, and the high plateau of Tibet hold almost no one. Meanwhile a few patches glow: the plains of eastern China, the Ganges valley of India, the island of Java, western Europe, and the eastern United States.

Geographers use population density to describe this. Density is simply people divided by land area. Bangladesh packs more than a thousand people into each square kilometer. Canada, which is far larger, averages about four. Illinois falls in between, with roughly ninety. But density hides as much as it shows. Most of Canada’s people live within a couple hundred miles of the U.S. border, and most of Illinois lives in the Chicago area, so a single average for the whole state is misleading.

Why the pattern? People cluster where they can grow food and reach one another. River valleys with rich soil fed the earliest cities, and they still hold huge numbers. Coasts allow trade. Mild climates with enough rain make farming reliable. Deserts, tundra, and steep mountains push people away. History then locks the pattern in: a city that grew because of a river keeps growing long after trains and trucks replace the boats, because the people, buildings and jobs are already there.

The word ecumene means the part of the Earth that people permanently inhabit. Over thousands of years the ecumene has spread as people learned to irrigate deserts, heat homes in the far north, and drain swamps. Chicago itself was built on marshy ground beside a sluggish river. Engineers raised whole streets and buildings by several feet in the 1850s and 1860s to make the city drain. Where people live is partly nature’s choice and partly ours.

For most of human history, populations barely grew. Families had many children, but many of those children died young, and famine and disease killed adults too. High births and high deaths canceled out. Then, starting in Britain around 1800 and spreading across the world, something changed. Clean water, sewers, vaccines, and better food made death rates fall. But birth rates did not fall at the same time. For a generation or two, families kept having six or seven children, and most of them now lived.

Geographers call this pattern the demographic transition, and they describe it in stages. In stage one, births and deaths are both high and the population is stable. In stage two, deaths drop while births stay high, and the population explodes. In stage three, births begin to fall as children survive, cities grow, and women get schooling and jobs. In stage four, births and deaths are both low and growth slows to almost nothing. Some geographers add a stage five, where births fall below deaths and the population shrinks, as in Japan and Italy today.

The model explains why the world grew so fast in the twentieth century. In 1900 there were about 1.6 billion people. By 2000 there were about 6.1 billion. That was not because people suddenly had more children. It was because far fewer of them died. Countries went through stage two one after another: Europe first, then Latin America and Asia, and much of sub-Saharan Africa now. Nigeria’s pyramid is a stage-two or early stage-three shape. Japan’s is stage five.

The total fertility rate, or TFR, is the key number. It is the average number of children a woman will have over her lifetime. A TFR of about 2.1 keeps a population steady, because each pair of parents is replaced by two children with a little extra for those who die young. The world’s TFR fell from about five in 1960 to about 2.3 today. The United States sits near 1.6, Illinois close to that, so American growth now comes mainly from immigration rather than births.

A population pyramid is really a bar chart turned on its side and folded in the middle. Each horizontal bar is an age group, usually five years wide. Males extend to the left, females to the right. The youngest are at the bottom. Three shapes appear over and over. A wide base and a narrow top means many children and rapid growth. Straight sides mean slow growth, with each age group about the same size. A narrow base and a thick middle or top means an aging, shrinking population.

The bars also record history. Look at Germany’s pyramid and you see dents where the two world wars killed young men and cut births. Look at China’s and you see a sudden narrowing below age forty-five. That is the mark of the one-child policy, which ran from 1980 to 2015. The United States pyramid has a bulge for people born between 1946 and 1964, the baby boom that followed World War II. That bulge is now moving into the top of the chart as those Americans retire.

Planners read pyramids to see what is coming. A wide base means a country needs schools now and jobs in fifteen years. A bulge in the twenties and thirties means a large workforce, which economists call a demographic dividend if the country can employ them. A thick top means rising costs for pensions and health care, with fewer workers to pay for them. The dependency ratio compares the number of children and retirees to the number of working-age adults. Both Nigeria and Japan have high ratios, but for opposite reasons.

Notice one more detail. In most countries the bars for women get longer than the bars for men at the oldest ages, because women on average live several years longer. In a few countries, including India and China, the bars for young boys are longer than for young girls, a sign that families have favored sons. A pyramid cannot tell you why, but it can tell you where to look.

In 1885 an English geographer named Ernst Ravenstein studied the British census and wrote down what he called laws of migration. Most migrants, he found, move only a short distance. Those who go far tend to head for big cities. Every flow of migrants produces a smaller flow back the other way. People from the countryside move more than city people, and young adults move most of all. His laws have held up surprisingly well for almost a century and a half.

In 1966 the American demographer Everett Lee gave the idea a simpler shape. Every place has push factors that drive people out: no jobs, war, drought, persecution, a flood. Every place has pull factors that draw people in: work, safety, family already there, good land, freedom. Between origin and destination lie intervening obstacles: distance, cost, a border, a sea, a language. A person migrates when the pushes and pulls together outweigh the obstacles. Change any of the three and the flow changes.

Geographers also sort migration by type. Internal migration is within one country, like a family moving from rural Illinois to Chicago. International migration crosses a border. Voluntary migration is chosen, even if the choice is hard. Forced migration is not: the Atlantic slave trade, the removal of Native nations along the Trail of Tears in the 1830s, and today’s refugees fleeing war are all forced. The United Nations counts a refugee as someone who has crossed a border to escape persecution or violence and cannot safely return.

One more pattern matters. Migrants rarely spread out at random. They follow relatives and neighbors to places where someone they know already lives, which is called chain migration. That is why Chicago has a Polish neighborhood, a Mexican neighborhood on the Southwest Side, and Devon Avenue on the North Side lined with Indian and Pakistani shops. Each chain started with a few people who wrote home and said: come.

In 1910 about forty-four thousand Black people lived in Chicago. By 1920 there were roughly one hundred nine thousand, and by 1930 about two hundred thirty-four thousand. This was the start of the Great Migration, the movement of about six million African Americans out of the South between 1910 and 1970. It was one of the largest internal migrations in American history, and it was driven by a clear set of pushes and pulls.

The pushes were brutal. Under Jim Crow laws, Black Southerners could not vote, were forced into segregated and inferior schools, and lived under the threat of lynching. Most farmed as sharecroppers, renting land and paying with a share of the crop, a system that kept families in permanent debt. In the 1910s the boll weevil, a beetle, destroyed cotton crops across the South, wiping out even that thin living.

The pulls came from the North. World War I cut off immigration from Europe just as factories needed workers, so Chicago’s steel mills, stockyards and railroads hired Black workers for the first time in large numbers. A job in a Chicago packinghouse paid several times what a sharecropper earned. The Chicago Defender, a Black newspaper carried south by railroad porters, printed job ads and stories of Northern life and urged readers to come. Letters home did the rest.

The obstacles did not disappear when the trains pulled into the Illinois Central station. Chicago confined Black families to a narrow strip on the South Side that became known as the Black Belt, through restrictive covenants that barred selling homes to Black buyers and through violence when they moved beyond it. In the summer of 1919 a riot killed thirty-eight people. Yet the migrants built churches, businesses, newspapers and music, and Chicago blues and gospel are among the results. A migration reshapes both the place people leave and the place they arrive.

About 280 million people now live outside the country where they were born. That is roughly three and a half percent of humanity. The United States has more immigrants than any other country, about forty-five million. Several smaller countries, though, have a higher share. The largest single flow in the world runs from Mexico to the United States. Other big flows run from South Asia to the oil states of the Persian Gulf, from North Africa and the Middle East into Europe, and from Ukraine after Russia’s invasion in 2022.

Most of this is economic. Ravenstein’s short-distance rule still holds inside countries, but the pull of a wage five or ten times higher can overcome an ocean. Migrants send money home, called remittances, and for countries like the Philippines, Guatemala and Nepal those transfers are one of the biggest sources of income. Most migrants are young adults, which is why they tend to fill jobs in construction, farming, care work and restaurants in the places they arrive.

War drives the rest. The United Nations counted more than 100 million forcibly displaced people in 2022, the most ever recorded. Some are refugees who crossed a border, from Syria, Afghanistan, Ukraine, Venezuela, South Sudan and Myanmar among others. More are internally displaced, uprooted but still inside their own country. Most refugees do not go to rich countries; they stay next door, in Turkey, Colombia, Pakistan, Uganda and Germany. Whether a migrant counts as a refugee or an economic migrant decides what rights they have, and the line is often argued.

Illinois is a case study. The state has about 1.8 million foreign-born residents, roughly one in seven people. Mexico, India, Poland, the Philippines and China are the leading birthplaces. Without them the state’s population would be falling, since Illinois has more people leaving for other states than arriving from them. Debates about migration in Illinois, like everywhere, turn on real trade-offs: wages and jobs, the cost of schools and services, and the law. Behind all of it is a simple fact: every migrant is a person who left home for a reason.

Linguists count about seven thousand living languages. Most are spoken by small groups, and hundreds have fewer than a thousand speakers left. A handful are giants: Mandarin Chinese has close to a billion native speakers, Spanish about half a billion, and English roughly four hundred million native speakers plus far more who learned it later. Languages that share a common ancestor form a language family, the way cousins share a grandparent.

The largest family by speakers is Indo-European, which stretches from Iceland to Bangladesh and includes English, Spanish, Russian, Persian, Hindi and Bengali. English mother, German Mutter, Latin mater, Sanskrit matar: the resemblance is not chance. These languages all descend from one spoken on the grasslands north of the Black Sea perhaps six thousand years ago. Sino-Tibetan, including Chinese, is the second largest family. Others include Afro-Asiatic, with Arabic and Hebrew; Niger-Congo, with Swahili and Yoruba; and Austronesian, whose speakers sailed from Taiwan to Madagascar, Hawaii and New Zealand.

A language spreads by diffusion. Relocation diffusion happens when speakers move, which is how English reached North America and Spanish reached the Andes. Expansion diffusion happens when a language spreads to new people without a mass migration, the way Latin spread through the Roman Empire or English spreads today through trade, science and the internet. Conquest, colonization and schooling have carried a few languages across the world while pushing many others toward extinction.

Illinois shows both patterns. The state’s name comes from a French version of a word used by the Illinois people, an Algonquian-speaking nation. French traders and priests named Des Plaines, Vincennes and Bourbonnais. English arrived with American settlers. Today about a quarter of Chicago households speak a language other than English at home, Spanish most of all, followed by Polish, Chinese, Tagalog and Arabic. A city’s street signs are a record of who came, and when.

Roughly a third of the world’s people identify as Christian, about two and a third billion. Nearly two billion are Muslim, about 1.2 billion are Hindu, and about half a billion are Buddhist. Around 1.2 billion say they belong to no religion, a group concentrated in China, Japan and parts of Europe. Judaism has about fifteen million followers but an outsized place in history, since Christianity and Islam both grew from its soil. Hundreds of millions more follow folk, traditional and smaller faiths.

Each faith has a hearth, the place it began. Judaism, Christianity and Islam all began in Southwest Asia, within a few hundred miles of one another. Hinduism and Buddhism began in the Indian subcontinent. From the hearth, religions spread the same ways languages do. Missionaries and traders carried Buddhism along the Silk Roads to China, Korea and Japan, and Islam along sea routes to Indonesia, now the largest Muslim-majority country. Conquest and colonization carried Christianity to the Americas and much of Africa. Hinduism spread far less, because it is tied to particular places, rivers and communities in India.

Geographers distinguish universalizing religions, which seek converts from anyone anywhere, from ethnic religions, which are bound to one people and place. Christianity, Islam and Buddhism are universalizing, which is why they cover the map. Hinduism, Judaism and Shinto are mostly ethnic religions. The distinction helps explain the pattern: a faith that sends missionaries spreads like ink; a faith you are born into moves only when its people move.

Religion writes itself on the landscape. A Chicago skyline holds church steeples and the domes of Orthodox cathedrals built by Greek and Ukrainian immigrants. There are minarets of mosques on the Southwest Side and in suburbs like Bridgeview. Hindu temples stand in Lemont and Aurora. The Baha’i House of Worship in Wilmette is one of only a few in the world. Cemeteries, holidays, food rules, and the days shops close all follow the same map. Religion is one of the strongest forces shaping where people gather and how they live together.

An ethnic group is a set of people who see themselves as sharing a common ancestry, history, language, or culture. Ethnicity is not the same as race, which sorts people by physical appearance. It is not the same as nationality either, which is citizenship in a state. A person can be ethnically Kurdish, a citizen of Turkey, and speak Turkish at school. Ethnicity is partly inherited and partly chosen, and it can shift over generations. That is why the grandchildren of Chicago’s Italian, Irish and Polish immigrants today mostly describe themselves simply as American.

Trouble comes when the lines on a map do not match the people inside them. Most of the borders in Africa and the Middle East were drawn by European powers between the 1880s and 1920s with little regard for who lived where. The Kurds, roughly thirty million people, were split among Turkey, Iraq, Iran and Syria. They have no state of their own. When Britain left India in 1947 it divided the land into India and Pakistan along religious lines. Roughly fifteen million people fled across the new border in a few months, and hundreds of thousands died in the violence.

The worst outcomes have names. Ethnic cleansing is the forced removal of a group from a territory. Genocide is the deliberate attempt to destroy a group. In Rwanda in 1994, over about one hundred days, Hutu extremists killed roughly eight hundred thousand people, mostly Tutsi, in a country where the two groups spoke the same language and lived side by side. In the former Yugoslavia in the 1990s, wars over which people belonged where killed more than one hundred thousand.

Yet ethnic diversity is not the cause of conflict by itself. Switzerland has four national languages and has been at peace for generations. Chicago has Mexican, Black, Polish, Chinese, Indian, Arab and Ukrainian neighborhoods within a few miles of one another. The difference lies in whether a state treats all groups fairly, whether power is shared, and whether leaders choose to inflame differences or manage them. Geography sets the stage; politics writes the script.

Culture is everything a group of people learns and passes on: food, clothing, houses, music, games, beliefs and manners. Geographers split it roughly in two. Folk culture belongs to a small, usually rural group, changes slowly, and is passed down in person. The Amish of central Illinois, with their horse-drawn buggies and plain dress, keep a folk culture on purpose. So do the quilting patterns, fiddle tunes and barn styles that vary from one valley to the next in Appalachia.

Popular culture is the opposite. It is produced for a mass market, spreads fast through media and trade, and looks much the same everywhere. A fast-food chain in Chicago, Cairo and Tokyo serves nearly the same menu. The same songs top charts on several continents in the same week. Pop culture diffuses hierarchically, jumping from big cities to smaller ones and skipping the countryside at first, and then contagiously, spreading person to person like a cold. Both kinds of culture are real culture; the difference is scale and speed.

Every culture writes itself on the land. Geographers call the result the cultural landscape: the visible marks people leave, from field patterns to skylines. Chicago’s bungalow belt, tens of thousands of brick single-family homes built between about 1910 and 1940, is a cultural landscape. So is the corn-and-soybean checkerboard of central Illinois, laid out on the square-mile grid that the Land Ordinance of 1785 imposed on the whole Midwest. So are the murals of Pilsen and the shrines in front yards on the Southwest Side.

The spread of popular culture raises real questions. When a global brand replaces local food, or English crowds out a language with five hundred speakers, something is lost that cannot be rebuilt. At the same time, popular culture carries new ideas, connects people across borders, and gives young people in small towns a window on the world. Geographers do not settle that argument; they map it, and ask who gains and who loses in each place.

Look back at the two pyramids. The single strongest predictor of a country’s birth rate is how many years its girls spend in school. Across the world, women who finish secondary school marry later, have fewer children, and are far more likely to see those children survive. In Niger, where most women have little schooling, the average woman has about six children. In neighboring countries where girls’ education has expanded, the rate has dropped much faster. Education changes what women can choose.

Geographers measure these gaps directly. Literacy rates for women still trail those for men in much of South Asia and sub-Saharan Africa, though the gap has narrowed sharply since 1990. Women do most of the world’s unpaid work, farming, hauling water, and caring for children and the old, which does not show up in a country’s income statistics at all. In many countries women cannot legally own land or open a bank account without a male relative’s permission. The United Nations tracks these differences in a Gender Inequality Index that combines health, schooling, jobs and political power.

Development moves when the gaps close. Economists have found that when women earn income, a larger share of it goes to children’s food and schooling. Women in Bangladesh’s garment factories, whatever the hard conditions, have driven a sharp fall in early marriage and birth rates since the 1990s. Rwanda, rebuilding after the 1994 genocide, wrote quotas for women into its constitution and now has one of the highest shares of women in any national legislature, above sixty percent.

The United States is not finished with these questions either. American women earn on average about eighty-two cents for every dollar men earn, partly because of the jobs they hold and partly because of pay for the same job. Women hold about a quarter of the seats in Congress. Illinois has elected women to the U.S. Senate and to the state’s top offices, and women make up more than half of the state’s college students. Development, here as anywhere, is not just about roads and factories; it is about who gets to use them.

In 1800 about three percent of the world’s people lived in cities. Around 2007 the share passed fifty percent, and by 2050 the United Nations expects it to reach about two-thirds. This shift from countryside to city is called urbanization, and it is one of the largest changes in human history. It is not finished. Most of the growth now is in Asia and Africa, where cities like Lagos, Dhaka and Kinshasa add hundreds of thousands of people a year, many of them arriving from villages with little more than a bag.

Cities grow where geography rewards them. Geographers speak of a city’s site, the actual ground it sits on, and its situation, its position relative to other places and routes. Chicago’s site was poor: a low, muddy plain that flooded. Its situation was superb. It sat at the one place where a short portage linked the Great Lakes water system to the Mississippi River system, so that a canoe, and later a canal boat, could pass from the Atlantic to the Gulf of Mexico. When railroads came in the 1850s they aimed at the same spot for the same reason.

The numbers show what a good situation is worth. In 1840 Chicago had about 4,500 people. By 1870 it had nearly 300,000. By 1900 it had 1.7 million, and it was the second-largest city in the country. No other city in the world had ever grown that fast for that long. Grain from the prairies, lumber from Wisconsin, cattle from the Plains and immigrants from Europe all passed through the same funnel, and each of them left a little behind.

Cities also arrange themselves into a hierarchy. A small town has a grocery store and a gas station. A county seat adds a hospital and a courthouse. A regional city adds a university and an airport. A few world cities, such as New York, London, Tokyo and, on most lists, Chicago, hold headquarters, financial markets and connections that serve the whole planet. The bigger the city, the rarer and more specialized the services it can support, and the wider the area it draws from.

In 1925 Ernest Burgess, a sociologist at the University of Chicago, drew the city as a bull’s-eye. At the center was the business district, the Loop. Around it lay a zone of factories and cheap housing where new immigrants first landed. Beyond that came a ring of working-class homes, then a ring of better houses, then a commuter zone of suburbs. As the city grew, each ring pushed outward into the next. This concentric zone model was the first attempt to explain the shape of a city rather than just describe it.

Burgess had drawn Chicago, and Chicago is not every city. In 1939 the economist Homer Hoyt studied rents in many American cities. He argued that land use grows in wedges, or sectors, along transportation lines rather than in rings. Factories follow a rail line or a river outward. Wealthy neighborhoods extend along a lakefront or a scenic ridge. Chicago fits this too: industry spread southwest along the river and canal, and wealth spread north along the lake. In 1945 Chauncy Harris and Edward Ullman added a third idea, the multiple nuclei model. In it a city has several centers, such as an airport, a university, a port and a mall district. Each pulls its own kind of activity.

None of the three is simply right. They are tools for asking why a neighborhood is where it is. Cities outside the United States often follow other patterns. In many Latin American cities the rich live near the center along a grand avenue and the poorest live in self-built settlements on the edge, the reverse of the American pattern. Many European cities keep their historic core, protect it with strict rules, and push tall buildings to the outskirts.

Two forces have reshaped American cities since Burgess drew his circles. Suburbanization after 1945, powered by cars, highways and federal home loans, moved millions of families outward. Chicago’s population peaked at about 3.6 million in 1950 and stands at about 2.7 million today, while its suburbs grew to hold more than twice that. More recently, gentrification has reversed the flow in some neighborhoods, as wealthier residents move into older areas near downtown, raising rents and pushing out long-time residents. Both processes are visible from the Willis Tower, one in every direction.

A city that grows faster than it can build is a hard place to live. Chicago in the 1880s had tenements without running water and streets of mud. Cholera and typhoid, carried by the city’s own sewage, killed thousands. Today the same story plays out in Lagos, Nairobi, Mumbai and Manila. About one billion people, roughly a quarter of all city dwellers on Earth, live in informal settlements. These are neighborhoods built by their residents on land they do not own. Most lack paved streets, sewers, or legal power and water connections.

Informal settlements are not simply slums. They are where a migrant from the countryside can afford to live, where small businesses start, and where communities organize. Dharavi in Mumbai, one of the densest places on the planet, holds thousands of small workshops recycling plastic, tanning leather and sewing garments. The problems are real: fires, floods, disease, eviction, and children who walk past open drains to school. The solutions that work best usually give residents legal title to their homes and then bring in water, sanitation and roads, rather than bulldozing the neighborhood.

Transportation shapes every city’s growth. Cities built around walking are compact and dense. Cities built around streetcars and subways, like Chicago’s Loop and the neighborhoods along the L lines, stretch along the rails. Cities built around cars, like Houston or Phoenix, sprawl for dozens of miles at low density. Sprawl brings bigger houses and yards but longer commutes, more pavement, and more fuel burned per person. Chicago has all three patterns in layers, which is why a trip across the region can take ninety minutes.

Cities also concentrate both wealth and poverty. Chicago remains one of the most racially segregated cities in the United States, a legacy of the covenants, redlining and public housing decisions described in the last chapter. Life expectancy in the Streeterville neighborhood is about thirty years longer than in Englewood, nine miles south. Geographers map these gaps because a map makes an argument: where you live in a city is one of the strongest predictors of how long you will live.

Most farmers in history grew food mainly to feed themselves. That is subsistence agriculture. Hundreds of millions of families in sub-Saharan Africa and South Asia still practice it. They work plots of a few acres with hand tools or an ox, and in a bad year they have no surplus to sell. The opposite is commercial agriculture: growing crops or animals to sell. A single Illinois farm family may work two thousand acres with a combine guided by satellites. It sells nearly everything it grows to buyers it will never meet.

The gap between the two has widened since the 1950s. The Green Revolution was led by the American scientist Norman Borlaug, who won the Nobel Peace Prize in 1970. It bred new high-yield wheat and rice and spread them across Mexico, India and Pakistan along with fertilizer and irrigation. Grain harvests in India more than doubled in a generation. Famines that had killed millions became rare. The costs came later: heavy fertilizer runoff, falling water tables where wells were overpumped, and small farmers who could not afford the new seeds and chemicals.

In rich countries farming has become agribusiness, an industry that stretches from seed companies and tractor makers through the farm to grain traders, food processors and supermarkets. Illinois is a case study. The state grows more soybeans than any other and trades with Iowa for first place in corn. Most of that corn never reaches a dinner plate as corn: it feeds hogs and cattle, becomes ethanol fuel, or is turned into sweeteners and starch. Chicago’s Board of Trade, founded in 1848, set the prices for the world’s grain for more than a century.

The geography of what grows where follows soil, climate and distance to market. Central Illinois has some of the deepest, blackest prairie soil on Earth, left by glaciers and ten thousand years of grass, so it grows corn and soybeans. Wisconsin, cooler and hillier, keeps dairy cows. California’s valleys, with irrigation, grow the vegetables and fruit that ship across the country. Florida grows oranges because it rarely freezes. Each region specializes, and the trucks and trains connecting them are as much a part of agriculture as the fields.

A factory is a decision about geography. Where should it sit? The German economist Alfred Weber argued in 1909 that a plant should go where the total cost of moving raw materials in and finished goods out is lowest. If the raw material is heavy and loses weight in processing, like iron ore becoming steel, build near the ore or the coal. If the product is bulkier or more fragile than its inputs, like bottled soda, build near the customers. Chicago’s steel mills rose on the southeast side of the city because ore from Minnesota came down the lakes by ship and coal came up from Illinois by rail, and the two met there.

For a century the map of industry was the map of coal and iron: the English Midlands, Germany’s Ruhr, the American belt from Pittsburgh through Cleveland and Detroit to Chicago and Gary. Then, from the 1970s on, that map came apart. Cheaper shipping containers, better communications, and trade agreements let companies split production across countries. Design might happen in California, chips in Taiwan, assembly in China or Vietnam, customer service in the Philippines. Geographers call this the global division of labor. Each step goes where it is cheapest to do well.

The results were uneven. Consumers worldwide got cheaper goods, and hundreds of millions of people in China, South Korea and elsewhere moved out of poverty into factory jobs. But in the old industrial belt, now often called the Rust Belt, mills and plants closed. Chicago lost most of its steel jobs; the Wisconsin Steel plant shut in 1980 and U.S. Steel’s South Works, once employing about twenty thousand, closed in 1992. Gary, Indiana, lost more than half its population. Whole neighborhoods built around a plant’s paycheck emptied out.

Manufacturing has not vanished from Illinois, but it has changed. The state still makes machinery, food products, chemicals and pharmaceuticals. Because of automation, those plants use far fewer workers than before. Meanwhile Chicago’s economy has shifted toward finance, law, health care, universities and logistics. Logistics is the business of moving goods, often through the same rail yards that once fed the stockyards. Recent policy debates about tariffs, supply chains and bringing production home all turn on the same question Weber asked in 1909: where should the factory go?

How do you compare the well-being of Norway and Niger? The oldest yardstick is gross domestic product per person: the value of everything a country produces in a year, divided by its population. By that measure Norway is among the richest countries on Earth, at roughly one hundred thousand dollars per person, and Niger among the poorest, at under one thousand. The United States sits near eighty thousand and India near two thousand five hundred. GDP per person is easy to compute and it tracks a great deal, from cars to hospitals.

But GDP misses things. It counts a dollar earned by a billionaire the same as a dollar earned by a farmer, so it says nothing about who gets the money. It ignores unpaid work at home. It counts pollution cleanup as production. And a country can be fairly rich and still leave many people sick and uneducated. In 1990 the United Nations began publishing the Human Development Index, which combines three things: income per person, life expectancy at birth, and years of schooling. Norway, Switzerland and Iceland usually rank near the top; Niger, Chad and South Sudan near the bottom.

The map of development has a shape. Rich countries cluster in North America, Europe, East Asia and Australia; the poorest cluster in sub-Saharan Africa and parts of South Asia. Older textbooks called these the developed and developing worlds, or the global North and South. Those labels blur a lot. China’s income per person has risen roughly tenfold since 1990. Within the United States, life expectancy in some counties trails that of much poorer countries. Development is a spectrum, and it moves.

Geographers argue about why the gap exists. Some point to geography itself: tropical disease, poor soils, landlocked positions far from ports. Some point to history: colonial rule that drew borders, extracted resources and left weak institutions. Some point to present policy: corruption, war, trade rules, and debt. Most likely all three matter, in different mixes in different places. What the measures show clearly is that the gap can close. Life expectancy in Africa has risen by more than a decade since 1990, and the share of the world in extreme poverty has fallen from more than a third to under a tenth.

Every city, farm and factory in this chapter runs on energy, and most of it comes from the ground. Coal, oil and natural gas, the fossil fuels, supply roughly eighty percent of the world’s energy. They are concentrated in a few places. Oil lies under the Persian Gulf, Russia, Venezuela, and the United States, which has become the world’s largest producer. Coal is mined in China, India, the United States and Australia. Gas comes from Russia, Iran, Qatar and the United States. Where the fuel is, and who controls the routes it travels, has shaped wars and alliances for a century.

Fossil fuels are nonrenewable: the Earth made them over millions of years and will not make more on any human timescale. Renewable sources, sun, wind, water, and heat from the Earth, do not run out, and their cost has fallen sharply. Solar panels cost roughly a tenth of what they did in 2010. Wind and solar now supply more than ten percent of the world’s electricity and are the fastest-growing sources. Nuclear power, which produces no carbon dioxide but leaves radioactive waste, supplies about ten percent of the world’s electricity as well.

Illinois is unusual. It generates more electricity from nuclear plants than any other state, from reactors along the Illinois, Mississippi and Rock rivers and near the Wisconsin line. Coal, mined in the state’s southern counties for two centuries, has fallen from most of Illinois’s power to a small share. Wind turbines now line the flat farmland of central Illinois, where they stand among the corn. Drive from Chicago to Springfield and you pass through most of the energy story in three hours.

The trade-offs are real. Fossil fuels are dense, portable and reliable, and the world’s cars, ships, planes and steel mills were built around them. They also produce carbon dioxide that warms the planet, and burning coal fouls the air; air pollution is estimated to cause millions of early deaths worldwide each year. Renewables are clean and increasingly cheap, but the sun sets and the wind drops, so they need storage or backup. Poorer countries argue they should not be asked to skip the cheap fuels that made rich countries rich. Every energy choice is a geography question: where is it, who needs it, and who bears the cost?

Only about two and a half percent of the Earth’s water is fresh, and most of that is locked in ice or deep underground. The Great Lakes hold roughly a fifth of the world’s surface fresh water, which is why Chicago has never had to worry about running dry. Much of the world is not so lucky. Cape Town, South Africa, came within weeks of shutting off its taps in 2018. The Aral Sea in Central Asia, once the fourth-largest lake on Earth, has mostly vanished since the 1960s because the rivers that fed it were diverted to grow cotton.

About seventy percent of the fresh water people use goes to farming, not to homes. That is the link between water and food. India and the United States both pump groundwater faster than rain refills it; the Ogallala Aquifer under the Great Plains, which waters wheat and corn from South Dakota to Texas, is dropping year by year. When water runs short, food does too. Food security means that everyone has reliable access to enough safe, nutritious food. By that standard, roughly one person in eleven worldwide still goes hungry, mostly in sub-Saharan Africa and South Asia, and mostly because of poverty and war rather than a global shortage.

The world grows enough food to feed everyone. The problem is who can get it. Famine today almost always happens where there is fighting: Somalia, South Sudan, Yemen. Farmers cannot plant, roads are cut, and aid cannot get through. Meanwhile about a third of the food produced worldwide is lost or wasted, in fields, in storage and in kitchens. Chicago’s own food deserts, neighborhoods far from any full grocery store, are a small version of the same problem: the food exists, but distance and cost keep it out of reach.

Water is also a border issue. Rivers do not stop at lines on a map. Egypt depends almost entirely on the Nile, whose water comes from Ethiopia, which finished a huge dam upstream in the 2020s. Turkey’s dams control much of the water reaching Syria and Iraq. India and Pakistan have shared the Indus under a treaty since 1960 despite wars between them. Even the Great Lakes are governed by an agreement among eight states and two Canadian provinces that limits how much water can be taken out of the basin. Who is upstream matters.

People have always changed the land: clearing forests, draining marshes, plowing prairie, damming rivers. Illinois once had about twenty-two million acres of tallgrass prairie; less than one hundredth of one percent survives. What is new is the scale. Since about 1850, burning fossil fuels has raised the amount of carbon dioxide in the air by roughly half, from about 280 parts per million to over 420. Carbon dioxide traps heat, and the Earth’s average temperature has risen a little over one degree Celsius, about two degrees Fahrenheit. That is the measured record, from ice cores, thermometers and satellites.

A degree does not sound like much, but it is an average across the whole planet, and it is not spread evenly. The Arctic has warmed about three times faster than the globe. Sea level has risen roughly eight inches since 1900 and is rising faster now, which matters most for low, crowded places like Bangladesh, the Nile delta, Miami and small Pacific islands. Heavier rain falls in some regions and longer droughts hit others. In Illinois, spring rains have grown heavier, flooding fields and basements, while summers bring more days above ninety degrees.

The costs fall unevenly too. The countries that burned the most fuel over the past two centuries are the United States and Europe first, then China. They are mostly better placed to cope. Many of the countries that burned the least, in Africa and South Asia, face the worst heat, drought and flooding with the fewest resources. This is why international climate talks are so hard. They are arguments about who should cut, who should pay, and who should be helped. The evidence gives no easy answer.

Sustainability means meeting today’s needs without leaving the next generation less to work with. Chicago has tried it in pieces: reversing the river in 1900 was not sustainable for the towns downstream, but the Deep Tunnel project, begun in the 1970s, now stores stormwater in more than one hundred miles of tunnels to keep sewage out of the lake. Green roofs cover City Hall. The Chicago River, once an open sewer, now has fish, kayaks and herons. None of that undoes the larger problem. But it shows that a city can change what it does to the land, and the water, once it decides to.

In geography, a state is not Illinois. It is a country: a defined territory with a permanent population, a government, and recognition by other states. There are about 195 of them. A nation is something different: a group of people who share a sense of common identity, usually through language, history and culture, and who feel they belong together. When one nation fills one state, as in Japan or Iceland, geographers call it a nation-state. Most states are not like that. They hold several nations, or a nation is split across several states, or both.

Borders are where the map gets argued over. Some follow rivers or mountain ridges, like the Rio Grande between Texas and Mexico or the Pyrenees between France and Spain. Some are straight lines drawn on a map by people who never saw the ground. Most of the border between the United States and Canada west of the Great Lakes is like that. It runs along the forty-ninth parallel for more than a thousand miles. Illinois’s own eastern border was drawn along a longitude line in 1818. Its northern border was pushed north from the tip of Lake Michigan so the new state would have a lakeshore. That is why Chicago is in Illinois and not Wisconsin.

Borders also fall apart and get redrawn. Since 1990 the map has changed a great deal. The Soviet Union split into fifteen states in 1991. Yugoslavia broke into seven. Czechoslovakia divided peacefully in 1993. South Sudan became the newest widely recognized state in 2011 after decades of war. Elsewhere borders are frozen in dispute: Kashmir between India and Pakistan since 1947, the line dividing Korea since 1953, and the borders of Israel and the Palestinian territories.

Inside a state, lines matter too. The United States divides power between the national government and fifty states, a system called federalism, and each state divides itself again into counties, cities, townships and districts. Illinois has 102 counties. Chicago has fifty wards, each electing an alderperson, and the lines of those wards are redrawn after every census. Where a line falls decides which school a child attends, which police respond, who collects the taxes and who gets to vote for whom. Political geography is the study of how those lines are drawn and what they do.

Lines on a map create both problems and solutions. Conflicts over borders come in a few familiar types. Some are about where the line is, like the disputed ridges between India and China. Some are about what the line cuts through: a nation split in two, a river shared, an oil field beneath both sides. Some are about who is inside it, when a group within a state wants its own, as in Catalonia in Spain, Scotland in the United Kingdom, or Quebec in Canada, each of which has voted on leaving. And some are about lines that no longer exist but that people remember.

The forces that pull a state together are called centripetal. Examples are a shared language, a national story, a strong economy, fair institutions, and a common threat from outside. The forces that pull it apart are centrifugal. Examples are regional inequality, ethnic or religious division, a government that favors one group, and geography that isolates a region. Every state has both. The United States survived a civil war over its own dividing line. It has argued ever since about how much power should sit in Washington and how much in the states.

States also cooperate, because most problems cross borders. The United Nations, founded in 1945, gives every recognized state a seat and a place to argue instead of fight, though its Security Council can act only when its five permanent members agree. The European Union has turned twenty-seven states into a single market with open internal borders. Trade agreements like the one linking the United States, Mexico and Canada set rules for goods that cross their lines. The Great Lakes agreement among eight states and two provinces is a smaller version of the same thing: shared water, shared rules.

Chicago lives on both sides of this. It is a global city whose airport connects it to every continent, whose grain and machinery cross oceans, and whose neighborhoods hold people from more than a hundred countries. It is also a city where ward lines, school boundaries and the state line with Indiana decide who pays for what. Human geography ends where it began, with a question: where should the lines go, and who gets to decide?