Unit 13 · Geography of the World

A ship’s captain in the middle of the Pacific sees nothing but water in every direction. How can she say exactly where she is? She uses two numbers. The first is latitude, how far north or south of the equator she is. The equator is the imaginary line that circles Earth halfway between the poles. Latitude is measured in degrees, from zero at the equator to ninety at each pole. Chicago sits at about 42 degrees north.

The second number is longitude, how far east or west she is. Longitude lines run from pole to pole like the sections of an orange. There is no natural starting line for east and west, so people had to agree on one. In 1884, delegates from many nations met in Washington and chose the line through the Royal Observatory at Greenwich, England, as the prime meridian, zero degrees. Longitude runs from zero to 180 degrees east or west of it. Chicago is at about 88 degrees west.

Put the two numbers together and you have a grid address that no one can mistake. Chicago is roughly 42 degrees north, 88 degrees west. Every phone that shows a blue dot on a map is quietly using these numbers. Sailors used to find latitude from the height of the sun at noon or the North Star at night. Longitude was much harder, because it needs an accurate clock, and good sea clocks were not built until the 1700s.

One more thing to notice. Latitude lines are all parallel and the same distance apart, about 111 kilometers per degree. Longitude lines are not. They are far apart at the equator and meet at the poles. That is why a map that draws both sets of lines as a plain square grid has to stretch the polar regions, which is where our map troubles begin.

A projection is the method a mapmaker uses to move the round Earth onto a flat sheet. The word comes from an old idea. Picture a glass globe with a light inside, and paper wrapped around it. The lines of the globe throw shadows onto the paper. Move the paper or the light, and the shadows change. Every projection keeps some things true and warps others. There is no way around it.

Mercator’s 1569 projection keeps directions true. A line of constant compass bearing is straight, which is why sailors used it for centuries. But it inflates the size of land far from the equator. Greenland looks as big as Africa when Africa is about fourteen times larger. Alaska looks larger than Mexico when Mexico is bigger. Antarctica smears across the whole bottom edge.

Equal-area projections, like the Gall-Peters map that became popular in the 1970s, keep sizes true but stretch shapes. Compromise projections, like Robinson’s map of 1963, split the difference and are a little wrong everywhere. Even the choice of what goes in the center is a choice. Most maps put Europe or the Atlantic in the middle. A map centered on the Pacific, common in Australia and Japan, shows the Americas on the right edge, and it is just as correct.

So when someone asks which map is the real one, the honest answer is the globe. Every flat map is a tool built for a purpose. Ask what the purpose was and you will understand what the map keeps true and what it gives up. A good map reader asks that question every time.

Look at a globe from above the Pacific and you see almost nothing but blue. About 71 percent of Earth’s surface is ocean. Geographers usually name five oceans: the Pacific, the Atlantic, the Indian, the Southern around Antarctica, and the Arctic around the North Pole. Really they are one connected body of water. The Pacific alone is larger than all the land on Earth put together.

The land is divided into seven continents: Asia, Africa, North America, South America, Antarctica, Europe and Australia. The word continent is partly a matter of custom. Europe and Asia sit on one solid piece of land, and some geographers call it Eurasia. Asia is by far the largest continent and holds well over half the world’s people. Australia is the smallest, and Antarctica has no permanent residents at all, only visiting scientists.

Between the continents and oceans lie smaller features that matter to the people who live near them. A peninsula is land with water on three sides, like Florida or Italy. An island is land surrounded by water on all sides. A strait is a narrow water passage between two larger bodies, like the Strait of Gibraltar between Spain and Africa. A gulf or bay is where the sea reaches into the land, like the Gulf of Mexico.

Illinois has no ocean, but it does touch one of the largest bodies of fresh water on Earth. Lake Michigan is one of the five Great Lakes, which together hold roughly a fifth of the world’s fresh surface water. Water from Lake Michigan eventually flows out through the other lakes, down the St. Lawrence River and into the Atlantic Ocean.

In 1912 a German scientist named Alfred Wegener stood in front of other scientists and made an odd claim. The continents, he said, were once joined and had drifted apart. His evidence was on the map. The east coast of South America fits into the west coast of Africa like puzzle pieces. The same kinds of rock and the same fossils of a small reptile appear on both sides of the Atlantic. Most geologists laughed. Continents plowing through solid ocean floor seemed impossible.

Wegener was right about the drift and wrong about the how. The answer came in the 1960s, when scientists mapped the ocean floor and found a chain of underwater mountains running down the middle of the Atlantic. New rock forms there as hot material rises from below and pushes the older floor outward. The floor spreads like two conveyor belts moving apart. The continents do not plow through it. They ride on it.

Today the idea is called plate tectonics. Earth’s rigid outer shell, the crust and the top of the layer below it, is broken into about a dozen large plates and several smaller ones. Beneath them is hot rock that slowly flows, and heat from Earth’s interior keeps it moving. The plates move a few centimeters a year, about as fast as your fingernails grow. Over millions of years that adds up to whole oceans opening and closing.

How do we know? Satellites can now measure the motion directly, and the numbers match what the rocks recorded. The Atlantic is getting wider by about two to three centimeters every year. If you could rewind two hundred million years, Africa and South America would slide back together, just as Wegener saw on his map.

Plates meet in three ways. Where two plates push together, the crust crumples upward. The Himalayas, the highest mountains on Earth, are still rising because the plate carrying India is ramming into Asia. Where plates pull apart, hot rock rises to fill the gap, as in the middle of the Atlantic and in the great rift valley of East Africa. Where plates slide past each other, they stick, strain and then jerk free. California’s San Andreas Fault is a boundary of that kind.

That jerk is an earthquake. Rock along a fault, a crack in the crust, stays locked for years while the plates keep pushing. When the strain becomes too great, the rock snaps and the ground shakes. Scientists measure the energy of a quake with a magnitude scale. Each whole step on the scale means about thirty-two times more energy released. A magnitude 7 quake is not a little stronger than a 5. It releases roughly a thousand times more energy.

A volcano is a place where melted rock, called magma, reaches the surface. Most volcanoes sit along plate boundaries, especially around the edge of the Pacific Ocean in a belt nicknamed the Ring of Fire. Japan, the Philippines, Indonesia, Alaska and the Andes all lie on it. Some volcanoes, like the ones that built the Hawaiian Islands, sit in the middle of a plate above a hot spot deep below.

Illinois sits far from any plate edge, so it is quiet most of the time. But not always. In the winter of 1811 and 1812 a series of huge earthquakes struck near New Madrid, Missouri, along an ancient buried fault. The shaking was felt across southern Illinois and rang church bells hundreds of kilometers away. The land there is still considered an earthquake risk today, which is why bridges and schools in southern Illinois are built to stricter rules.

Weather is what happens today. Climate is the pattern over many years. Chicago’s climate has cold winters and hot summers, even if one January afternoon happens to be mild. Four things do most of the work in setting a climate. The first is latitude. Near the equator the sun shines almost straight down all year, so it is hot. Near the poles the sun’s rays arrive at a low slant and spread over more ground, so it is cold.

The second is altitude, height above sea level. Air gets colder as you climb, by about six or seven degrees Celsius for every thousand meters. That is why Mount Kilimanjaro in Tanzania has snow on top even though it stands near the equator. Quito, the capital of Ecuador, sits almost on the equator but is cool all year because it is nearly three thousand meters up.

The third is the ocean. Water heats and cools slowly, so places near the sea have milder winters and cooler summers than places deep inside a continent. Ocean currents move heat too. The Gulf Stream carries warm water from the Gulf of Mexico across the Atlantic, which helps keep western Europe warmer than places at the same latitude in Canada. Chicago, far from any ocean, swings from below freezing to above thirty degrees within a single year.

The fourth is wind and the mountains that block it. Winds carry moisture from the ocean over land. When moist air hits a mountain range it rises, cools and drops its rain on the windward side. The far side, called the rain shadow, stays dry. The Cascade Mountains in Washington and Oregon are like that: green rainforest to the west, sagebrush desert to the east.

Around 1900 a German-Russian scientist named Wladimir Köppen noticed that the plants growing in a place tell you its climate. Where palms grow it is always warm. Where only mosses and small shrubs grow it is cold. He used temperature and rainfall to draw a world map of climate zones, and geographers still use a version of his map today.

The main zones run roughly in bands. Tropical climates near the equator are warm all year, some rainy every month and some with a wet and a dry season. Dry climates, deserts and the grasslands around them, get little rain, and many sit around 20 to 30 degrees north and south, where sinking air keeps skies clear. The Sahara, the deserts of Australia and the American Southwest are all in those bands.

Temperate climates have real seasons, with warm summers and cool or cold winters. Most of the United States, Europe, China and Japan are temperate. Illinois has a temperate climate with a sharp difference between seasons because it is far from the ocean. Farther north come the cold climates with long winters, like most of Canada and Russia, and finally the polar climates, where the warmest month never gets above ten degrees Celsius.

Mountains break the pattern. A tall peak in the tropics can pass through every zone on the way up, from rainforest at the base to ice at the top. That is why climate maps show highland zones as their own color. A zone is a useful label, but the real world is patchier than any map.

Stand in the Amazon rainforest and you are in shade at noon. Trees rise thirty meters or more, and their leaves lock together into a roof called the canopy. It rains almost every day. A biome is a large region with a particular climate and the living things suited to it. The tropical rainforest is the biome with the most kinds of plants and animals on Earth. Rainforests grow in South America, central Africa and Southeast Asia, wherever it is hot and wet all year.

Move away from the equator and the rain becomes seasonal. The forest opens into savanna, grassland with scattered trees, like the plains of East Africa where zebras and elephants graze. Farther still the rain nearly stops, and you reach desert. The Sahara, the largest hot desert, stretches across northern Africa and is roughly the size of the United States. Deserts are not always hot. The cold, dry heart of Asia is desert too.

In the temperate zones, rain decides whether you get forest or grassland. Where rain is plentiful, forests of oak, maple and beech drop their leaves each fall. Where it is drier, grasses take over. Illinois was once mostly tallgrass prairie, a temperate grassland with grass taller than a person and soil deep and black from thousands of years of roots. Almost all of it is now farmland, which is the same rich soil put to a new use.

Farther north, the forest turns to spruce and pine that keep their needles through long winters. This is the boreal forest, or taiga, which circles the globe through Canada, Scandinavia and Russia. Beyond it lies the tundra, where the ground stays frozen a short way down all year and only mosses, lichens and low shrubs survive. Then comes ice. The same sequence, rainforest to tundra, repeats going up a tall mountain.

Rain falls on a cornfield near Peoria. Some soaks in. The rest trickles into a ditch, then a creek, then a tributary stream, then the Illinois River, then the Mississippi, and finally the Gulf of Mexico near New Orleans. The land that drains into one river system is that river’s watershed. The Mississippi watershed is enormous. It collects water from thirty-one states, about forty percent of the land in the lower forty-eight, from the Rocky Mountains to the Appalachians.

Watersheds are separated by high ground called divides. The most famous in North America is the Continental Divide along the Rockies. Rain falling on its west side ends up in the Pacific. Rain on its east side heads for the Atlantic or the Gulf. Chicago sits on a much smaller divide. Water on one side flows to Lake Michigan and out to the Atlantic. Water on the other side flows to the Mississippi. The two are only a few kilometers apart.

The world’s great rivers built the world’s early civilizations. The Nile, the Tigris and Euphrates, the Indus and the Yellow River all fed farmers with water and rich mud from floods. The Nile and the Amazon are the longest rivers on Earth, each about 6,500 kilometers. The Amazon carries far more water than any other river, about a fifth of all the river water that reaches the world’s oceans.

Because a watershed connects everything upstream to everything downstream, what one town does affects another. In 1900 Chicago reversed the flow of the Chicago River so that its sewage would run toward the Mississippi instead of into Lake Michigan, the city’s drinking water. Cities downstream on the Illinois River were not pleased. Fertilizer washing off farms in Illinois today feeds a low-oxygen dead zone in the Gulf of Mexico. The river remembers everything.

A natural hazard is a natural event that can hurt people: an earthquake, a hurricane, a tornado, a flood, a volcanic eruption, a drought. Geography decides where each one is likely. Earthquakes cluster along plate boundaries. Hurricanes form over warm tropical oceans and strike the coasts of the Gulf, the Caribbean and East Asia. Tornadoes are most common where warm, wet air from the Gulf of Mexico meets cold, dry air from the north, which is exactly the middle of the United States.

Illinois knows tornadoes well. On March 18, 1925, the Tri-State Tornado tore across Missouri, southern Illinois and Indiana for more than three hours. It killed about 695 people, more than any other single tornado in American history, and wiped the town of Murphysboro, Illinois, nearly off the map. Illinois also floods. In the summer of 1993 the Mississippi and its tributaries rose over their banks for weeks and drowned farms and towns across the Midwest.

The same event does not do the same damage everywhere. A strong earthquake in Japan, where buildings are built to sway and schools drill for quakes, often kills few people. A weaker quake in a poor city of unreinforced brick can kill thousands. The hazard is nature’s. The disaster is partly ours. Building codes, warning sirens, weather radar, levees and evacuation plans all turn a deadly event into a survivable one.

Preparation is also about maps. Flood maps tell a family whether its house sits where the river will spread. Tornado shelters are marked on school maps. After the Indian Ocean tsunami of 2004 killed more than two hundred thousand people, nations around that ocean built a warning system with sensors and sirens. The geography of danger has not changed. What changed is how much people know about it.

In the summer of 1854 a deadly disease called cholera swept through a neighborhood in London. Doctors at the time blamed bad air. A physician named John Snow had a different idea. He walked the streets and marked every death on a map with a short black bar. The bars piled up around one public water pump on Broad Street. Snow’s map argued, without a single sentence, that the water was the killer. The pump handle was removed, and the idea that disease could travel in water gained ground.

Snow’s map made an honest argument. Maps can also make a misleading one. A map that colors whole countries a single shade hides the differences inside them. A map of election results colored by county makes a thinly settled countryside look like it outweighs a crowded city. A map with a bold red arrow makes an army look like it is already winning. Choosing the projection, the colors, the center and the title is choosing the message.

Maps have also been used to do harm. In the 1930s a federal agency drew maps of American cities, including Chicago, that shaded neighborhoods by how safe they were thought to be for home loans. Neighborhoods where Black families lived were colored red and marked as risky. Banks then refused loans there for decades. The practice is called redlining, and its effects on wealth and housing are still visible on maps of Chicago today.

So read a map the way you read an essay. Who made it, and when? What is it for? What does it show, and what does it leave out? Would a different projection, a different color scale or a different center tell a different story? A map cannot answer these questions for you. That is your job as its reader.

Look at a nighttime photograph of Earth taken from space. The lights are not spread evenly. They crowd along coasts, trace the paths of rivers and fill a few broad plains, while huge regions stay dark. Egypt is a clear example. Almost all of its more than one hundred million people live along the Nile River and its delta, a green ribbon in a brown desert. Away from the river the land cannot feed anyone.

Three things pull people to a place. The first is fresh water, for drinking and for crops. The second is good soil, especially the flat, deep soil of river valleys and old grasslands like the Illinois prairie. The third is access, a coast or a navigable river that makes it easy to move goods and people. The great cities of the world, from Shanghai to New York to Mumbai, almost all sit on a coast or a major river.

Places that lack these things stay thinly settled. Deserts, high mountains, dense rainforest and the frozen north hold few people. About half the world’s population lives in East and South Asia, where monsoon rains and river plains have fed dense farming for thousands of years. Australia is nearly the size of the United States but has fewer people than Texas, because most of its interior is dry.

Chicago exists where it does for these same reasons. The site is flat and the soil around it is some of the richest on Earth. Lake Michigan gave it fresh water and a harbor. The short portage between the Chicago River and the rivers flowing to the Mississippi made it the natural link between the Great Lakes and the whole interior of the continent. Geography did not build the city, but it chose the spot.

For most of human history there were fewer people on the whole planet than live in the United States today. Around the year 1800 the world’s population reached about one billion for the first time. Then it took off. Two billion came around 1927, three billion around 1960, and eight billion in 2022. The reason was not more babies. It was fewer deaths, as clean water, vaccines, better farming and modern medicine let far more children live to grow up.

Growth is now slowing. In many countries, including the United States, Japan and most of Europe, families have two children or fewer, and populations are aging. Most growth today comes from Africa and parts of South Asia, where families are larger and populations are young. Geographers study these patterns because they shape everything from how many schools a country needs to how much food it must grow.

Population density tells you how crowded a place is: the number of people divided by the land area. Bangladesh packs more than a thousand people into each square kilometer. Canada, one of the largest countries on Earth, has about four. Illinois has roughly ninety, but that average hides a lot. Chicago’s neighborhoods hold thousands per square kilometer, while some downstate counties have fewer than ten.

A high density is not good or bad by itself. Dense cities can be efficient, with short trips, shared transit and lively streets. They can also be crowded, expensive and polluted. Empty land can mean freedom and quiet, or it can mean a long drive to the nearest hospital. What matters is whether the place can support the people who live there.

In the early 1900s a young man in a village in southern Italy packed one bag and boarded a ship for New York. A young woman in Mississippi in 1917 bought a train ticket to Chicago. A family in Syria in 2015 walked toward the Turkish border. Each of them was a migrant, a person who moves to live in a new place. Geographers describe why with two words: push and pull.

Push factors are the things that drive people out. War, hunger, drought, floods, no jobs, unfair laws or violence against their group. Pull factors are the things that draw them somewhere else. Jobs, safety, land, schools, family already there, or simply the chance to be treated as an equal. Usually both are at work at once. The Italian villager was pushed by poverty and pulled by factory wages. The woman from Mississippi was pushed by racist laws and violence and pulled by Chicago’s steel mills and stockyards, which were hiring.

That second story is part of the Great Migration. Between about 1916 and 1970, roughly six million Black Americans left the South for cities in the North and West. Chicago’s South Side became one of their main destinations. They built churches, newspapers, businesses and the music called Chicago blues. They also met new barriers, from crowded housing to the redlining maps you read about earlier.

Migration changes both ends of the trip. The place people leave loses workers, often the young and ambitious, but gains money they send home. The place they arrive in gains labor, new food, new languages and new ideas, and sometimes tension with people already there. Chicago’s history is a stack of such arrivals: Irish and German, then Polish and Italian, then Black Southerners, then Mexican and now many others. Each layer is written on the city’s map, one neighborhood at a time.

Culture is the whole way of life a group of people shares: their language, food, religion, music, clothing, holidays and ideas about right and wrong. It is learned, not inherited. A baby born in Seoul and raised in Chicago grows up with Chicago’s culture. Geographers draw culture regions, areas where people share many of these traits. Latin America, where Spanish and Portuguese are spoken and most people are Catholic, is one. The Arab world, from Morocco to Iraq, is another.

Language is the clearest marker. Roughly seven thousand languages are spoken on Earth, though most have few speakers and many are vanishing. Mandarin Chinese has the most native speakers. English is spoken as a first or second language in more countries than any other, a legacy of the British Empire and American influence. Spanish is the main language across most of the Americas south of the United States. Languages come in families: Spanish, French, Italian and Portuguese all grew out of Latin, which is why they share so many words.

Culture regions have no sharp edges. Along the United States border with Mexico, Spanish and English mix in the same sentence. In Switzerland, four languages are official. In India, the government recognizes twenty-two languages and hundreds more are spoken. A map that paints each country one color hides all of that. A better map would use many colors, and they would bleed into one another.

Chicago is a small map of the world’s languages. Spanish is spoken in hundreds of thousands of homes. Polish has been common on the Northwest Side for more than a century. Chinese, Arabic, Tagalog, Urdu, Korean and dozens more are heard in neighborhoods, stores and schools. Your classroom probably contains more languages than some countries do.

Every major religion has a birthplace you can point to on a map. Judaism, Christianity and Islam all began in the Middle East. Hinduism grew up along the rivers of northern India, and Buddhism began there too, when a prince named Siddhartha Gautama became a teacher around the fifth century BCE. Where a religion is today is a story of how it traveled.

Religions moved with people. Buddhism followed traders and monks along the Silk Road into China, Korea and Japan, and by sea to Southeast Asia. Islam spread from Arabia in the 600s and 700s with armies and then with merchants, reaching Spain in the west and, by sea, Indonesia in the east, which today has more Muslims than any other country. Christianity spread across the Roman Empire and, after 1492, across the Americas with European colonists and missionaries.

Today Christianity has the most followers, roughly two and a half billion, followed by Islam with roughly two billion. Hinduism has more than a billion, nearly all in India and nearby. Buddhism has several hundred million, mostly in East and Southeast Asia. Many people follow local traditional religions, and more than a billion follow no religion at all. Every count is a rough estimate, because belief is hard to count.

Religion shapes the landscape. It decides what buildings rise highest in a town, a church steeple, a minaret or a temple tower. It sets holidays, foods and rules about the week. It can bind people together, and it has divided them too, in wars from the Crusades to the partition of India in 1947. A geographer’s job is not to judge any of it, but to see where it is and ask how it got there.

A natural resource is anything from the earth that people find useful: water, soil, trees, fish, wind, sunlight, coal, oil, iron, copper. Where they lie is a matter of geography, not fairness. Saudi Arabia sits on a vast pool of oil. Chile’s mountains hold more copper than anywhere else. The Democratic Republic of the Congo has most of the world’s cobalt, a metal inside every phone battery. Illinois has some of the deepest, richest farm soil on the planet and large beds of coal underneath it.

Resources come in two kinds. Renewable resources grow back or never run out if they are used with care: forests, fish, fresh water, wind, sunlight and the soil itself. Nonrenewable resources formed over millions of years and cannot be replaced once used: coal, oil, natural gas and metals. Every gallon of gasoline burned is gone for good. A forest cut down can regrow, but only if someone lets it.

Renewable does not mean unlimited. Cod fishing off Newfoundland in Canada was one of the richest fisheries on Earth for four hundred years. Boats took more fish than the sea could replace, and in 1992 the fishery collapsed and had to be closed. Tens of thousands of people lost their work. The Illinois prairie was renewable too, but plowing it took a century of topsoil away in some fields faster than it can rebuild.

Having resources is not the same as being rich. Some countries with huge oil wealth have many poor citizens, because the money goes to a few. Japan has almost no oil, coal or iron of its own and is one of the wealthiest countries in the world, because it imports raw materials and sells what its people make from them. What people do with what they have matters as much as what geography gave them.

Economists sort work into three groups. Primary work takes things straight from nature: farming, fishing, logging, mining. Secondary work makes things from those raw materials: a steel mill, a bakery, a shoe factory. Tertiary work, also called services, does things for people rather than making objects: teaching, nursing, driving a bus, coding software, cutting hair. The mix of the three tells you a lot about a place.

Two hundred years ago nearly everyone on Earth did primary work, mostly farming. Today in the United States fewer than two people in a hundred farm, yet the country grows more food than ever, because machines, fertilizer and better seeds let one farmer do the work of many. Illinois is a giant of primary work: it is usually first or second in the nation for corn and soybeans. But most Illinoisans are nowhere near a field. About four in five American workers now do service jobs.

Places specialize according to their geography. Iowa and Illinois farm because of their soil. Pittsburgh made steel because coal and iron ore were nearby and rivers could move them. Gary, Indiana, and the south side of Chicago made steel for the same reason. Bangalore in India became a center for software because of its universities and a language, English, shared with customers overseas. When the geography or the technology shifts, the work shifts, and towns built on the old work can be left behind.

In poorer countries most people still farm, often small plots by hand. As countries grow richer, workers move from farms to factories to offices, and from villages to cities. That shift is the story of Chicago’s own stockyards and steel mills, which employed tens of thousands and are now nearly all gone, replaced by hospitals, banks, universities and warehouses.

For more than a thousand years, silk, paper and spices moved west from China along the paths called the Silk Road. Glass, silver and horses moved east. No single trader went all the way. Goods passed from hand to hand through oasis towns in Central Asia. Each town grew rich from the passing traffic. Samarkand, in what is now Uzbekistan, was one of the most splendid cities in the world. It sat at the right spot on the route.

Sea routes carried far more. Ships on the Indian Ocean rode the monsoon winds. These blow toward India in summer and away from it in winter. They linked East Africa, Arabia, India and Southeast Asia. After 1492 the Atlantic became a highway. The exchange across it brought corn, potatoes and tomatoes to Europe and horses and wheat to the Americas. It also carried, in chains, more than twelve million enslaved Africans to plantations in the New World. Trade routes have never been only about goods.

Canals and railroads cut new routes through the map. The Suez Canal opened in 1869. It let ships go from Europe to Asia without sailing around Africa. The Panama Canal opened in 1914 and did the same between the Atlantic and Pacific. In Illinois, the Illinois and Michigan Canal was finished in 1848. It linked Lake Michigan to the Illinois River. Within a few years railroads turned Chicago into the meeting point of the East and the West.

The biggest change in modern trade fits in a steel box. In 1956 an American trucker named Malcom McLean loaded truck trailers onto a ship. The shipping container was born. A crane can now move a sealed box from ship to train to truck. No one touches what is inside. Shipping costs fell so far that it became cheap to make a shoe in Vietnam and sell it in Chicago. The map of trade today is a map of deep-water ports and rail yards.

Globalization is the word for a world in which goods, money, people and ideas move quickly across borders. The sneakers in the chapter story are a small case of it. Cotton from one continent, oil from another, rubber from a third, assembly in a fourth, design in a fifth, and a customer in a sixth. Each step happened where it was cheapest or best to do, and a container ship and a computer network tied them together.

Globalization has clear benefits. Shoes, phones and clothes cost far less than they would if everything were made at home. A factory job in Vietnam often pays more than farming did, and countries like South Korea and China have lifted hundreds of millions of people out of poverty in a few decades by making things for the world. Illinois farmers sell soybeans to China and Illinois companies sell tractors and machinery around the globe.

It also has costs, and they fall unevenly. Factories that left Chicago and Gary took steady jobs with them, and some neighborhoods never recovered. Workers in some overseas factories have faced long hours, low pay and unsafe buildings. When a factory in one country closes, a town on the other side of the world can go quiet. And every container ship burns fuel, so a cheap shoe carries a hidden cost in the air.

People argue about what to do. Some want tariffs, taxes on imports, to protect jobs at home. Others say tariffs raise prices for everyone and invite other countries to tax our goods in return. Some push for rules that require fair wages and safe factories abroad. Others worry those rules could cost the very workers they aim to help. There is no map that settles this. There is only the evidence, and the trade-offs people are willing to make.

Around 2007, for the first time in history, more people lived in cities than in the countryside. Today the largest urban areas hold tens of millions each. Tokyo’s metropolitan area has about thirty-seven million people, more than the whole state of Illinois three times over. Cities grow because they concentrate jobs, schools, hospitals and chances to meet people who know things you do not. A city is a machine for bringing people together.

That concentration creates problems. Housing runs short and prices rise, pushing poorer families to the edges or into crowded conditions. In many fast-growing cities of Africa, Asia and Latin America, millions live in informal settlements built without permits, often without piped water or sewers. Traffic clogs streets. Cars, factories and cooking fires foul the air. Delhi and Beijing have suffered days when the smog hid the sun. Water systems built for one million must serve ten.

Cities also solve problems. Chicago burned in 1871 and rebuilt with steel-framed towers that changed the way cities are built everywhere. It reversed its river to protect its drinking water, built a park system along the lake and laid out an elevated train, the L, that still moves hundreds of thousands of riders a day. Every city is a running argument about how to share limited space, and the arguments show up on the map as parks, highways, transit lines and the neighborhoods they cut through.

Geographers study the layout of a city to read those choices. Where are the highways, and whose neighborhoods did they split? Where are the grocery stores, and which areas have none? Where does the transit go, and where does it not? A map of a city is a map of who was listened to.

In 1960 the Aral Sea in Central Asia was the fourth largest lake in the world. Soviet planners then diverted the two rivers that fed it to irrigate cotton fields in the desert. The cotton grew. The sea shrank. By the 2000s most of it was dry salt flat, fishing towns sat kilometers from any water, and dust storms carried salt and chemicals across the region. It is one of the clearest lessons in geography: change one part of a landscape and the rest changes with it.

The United States has its own examples. In the 1930s farmers on the southern Great Plains plowed up grassland that had held the soil for thousands of years. Then drought came, and the wind lifted the loose dirt into black clouds that darkened the sky as far as Chicago and Washington. The Dust Bowl drove hundreds of thousands of families off their farms. Afterward, new methods of plowing, planting windbreaks and leaving cover on fields helped the soil stay put.

Not every change is a disaster, and none is free. Illinois drained its wetlands to make some of the most productive farmland on Earth, and lost most of the marshes that once filtered water and sheltered birds. Dams give cheap electricity and stop floods, and they also drown valleys and block fish. Cities pave land and give people homes. Every choice moves something on the map.

Today the largest human change is to the atmosphere itself. Burning coal, oil and gas since the 1800s has raised the amount of carbon dioxide in the air, and global average temperatures have risen. Scientists agree on that measurement. What to do about it is argued: how fast to switch to other energy, who should pay, and how to protect the workers and towns that depend on the old fuels. Those are questions of values as well as facts, and citizens, not maps, will have to answer them.