People & places

Why did the earliest cities grow beside rivers? Because a settlement needs two things before anything else. The first is fresh water, for drinking and for crops. The second is fertile soil, earth rich enough to give heavy harvests. The Nile, the Tigris and Euphrates, and the Indus offered both, because every year their floods spread fresh mud over the fields. On such land a few farmers could feed many other people, who were then free to become builders, traders and scribes.

Even the best land has a limit. The largest population that a place can support without running short of water, food or fuel is called its carrying capacity. It is not fixed. A new well, a canal or a better plough raises it, and a drought or exhausted soil lowers it. When people outgrow it, hunger and quarrels follow, or they move on.

Water and soil explain where farmers settle. They do not explain Makkah, which stands in a dry valley with almost no farmland. Pilgrims came to the Kaaba from all over Arabia, and its people, the Quraysh, were merchants, whose caravans went south to Yemen in winter and north to Syria in summer. Geographers separate a settlement’s site, the ground it stands on, from its situation, its position in relation to other places. Makkah’s site gave it little to grow. Its situation, between the markets of Yemen and Syria, gave its merchants their trade.

Trade explains a wider pattern too. Carrying goods by sea is far cheaper than hauling them overland, so a good harbour opens a town to distant markets. That is why many of the world’s largest cities stand on a coast, and why about 40 per cent of humanity lives within a hundred kilometres of the sea.

A society can be described in numbers, and the study that does so is demography: the statistics of human populations, their size, their ages and how they change. Only three things can change the size of a population. People are born, people die, and people move in or out.

Demographers measure the first two as rates, so that large and small countries can be compared. The birth rate is the number of babies born in a year for every thousand people, and the death rate is counted in the same way. Niger has a birth rate above 40. Japan’s is about 6. When births outnumber deaths, a population grows without any migration at all, and that growth is called natural increase. When deaths outnumber births, as in Japan since 2007, it shrinks unless newcomers arrive.

For most of history both rates were high. Families had many children and buried many of them, so populations grew slowly if at all. Then, in country after country, the same sequence unfolded. Demographers call it the demographic transition, and it has four stages.

In the first, births and deaths are both high. In the second the death rate falls, as clean water, better food and medicine keep children alive. In the third the birth rate falls too, as parents come to expect that their children will live. In the fourth both are low. Deaths fall before births do, and in the gap between them the population surges. The world’s population took all of history to reach one billion, around 1800. It passed eight billion in 2022.

The third way a population changes is by people moving. Migration is a move to live in a new place, and geographers explain it with two kinds of force.

Push factors are whatever drives people away from where they are: war, drought, a failed harvest, no work. Pull factors are whatever draws them toward somewhere else: wages, safety, land, family already there. Most moves have both at work, a shove from behind and a tug from in front, and people weigh them against the cost and danger of the journey.

Most migrants do not cross the world. They move from the countryside to the nearest city, or to a neighbouring country. Even so, about 304 million people, roughly one person in every twenty-seven, now live outside the country where they were born.

One journey has two names. Seen from the country a person leaves, it is emigration. Seen from the country they enter, it is immigration. The first drains a homeland of workers and the second brings them to a new land, which is why the same move can be mourned in one place and argued over in another.

Not every migrant chose to go. A refugee is someone who has fled their own country because of war or persecution and cannot safely return, and international law has protected such people since 1951. By the end of 2024 about 123 million people had been forced from their homes, most of them still inside their own countries.

Some scattered peoples keep their identity for generations. A people living far from its homeland, across many countries, yet still bound to it by memory and custom, is called a diaspora.

What becomes of a migration depends on how the newcomers are received. Often the people already there see them as ‘them’ and not ‘us’, and the newcomers meet prejudice: an unfavourable judgement of a whole group, formed before any one of its members is known. It often weakens when people get to know one another.

The founding migration of Muslim history shows another way. In 622 the Prophet and the first Muslims, persecuted in Makkah, moved north to Madinah, a journey of more than 300 kilometres. This move is the Hijra, and the Islamic calendar counts its years from it. The emigrants arrived with little. The Prophet paired them as brothers with the Muslims of Madinah, who are remembered as the helpers, and the helpers shared their homes and their harvests with them. Out of strangers and hosts he made one community.

A map is a picture of the Earth’s surface seen from above and shrunk to fit a page. Two decisions shape every one. The first is scale, the fixed ratio between a distance on the map and the same distance on the ground. At a scale of one to fifty thousand, one centimetre on the paper stands for half a kilometre of country. A map of a continent must leave almost everything out.

The second is how to flatten a globe. The skin of a sphere cannot be laid flat without stretching or tearing, so every flat map distorts something: areas, shapes, distances or directions. Each way of doing it is called a projection. Mercator’s, drawn in 1569, keeps compass directions true for sailors at the price of swelling the far north. On it Greenland looks as large as Africa, which is really fourteen times bigger.

How could a mapmaker of the twelfth century find out what distant lands were like? Around 1138 Roger II, the Norman king of Sicily, invited the Muslim geographer al-Idrīsī to his court at Palermo and set him a task: describe the whole known world. Al-Idrīsī did not rely on old books alone. For some fifteen years he gathered his facts by questioning experienced travellers, merchants and sailors who passed through Sicily, and he kept only what they agreed on.

The result, finished in 1154, was a book of seventy regional maps with a description of each region, and a great world map engraved on a disc of silver. It set out Europe, North Africa and Asia together in great detail. To modern eyes it looks upside down, because al-Idrīsī, like most Muslim mapmakers of his time, put south at the top.

How large is the whole Earth? About 1020 the scholar al-Bīrūnī measured it from a single mountain. At Nandana, in what is now Pakistan, he first worked out the mountain’s height. From its top he then measured how far the horizon of the plain below dipped beneath a level line of sight. That one small angle, the dip of the horizon, with the mountain’s height and some trigonometry, gave him the radius of the Earth. As his units are usually converted, his result is within a few per cent of today’s figure.

He was as careful about people. In India he learned Sanskrit and read the Hindus’ own books, and around 1030 he wrote an account of their beliefs and customs as they themselves understood them. A study of this kind, describing a people’s way of life from within, is now called an ethnography.

Geographers sort the places where people live into two broad kinds. Rural places are open country: farms, fields and villages, with people thinly spread. Urban places are towns and cities, where people live packed together and few of them grow food.

For nearly all of history, almost everyone was rural. By each country’s own count, fewer than a third of the world’s people lived in towns and cities as late as 1950. Around 2007 the urban share passed half for the first time, and it is now about 58 per cent and still rising. The cause is push and pull at work inside countries. Farms need fewer hands as machines arrive, and cities offer wages, schools and hospitals. Yet a city depends entirely on the countryside it draws people from, since nearly every meal eaten in a city was grown outside it.

The land also shapes how people make a living. Where rain is too scarce for crops, people have long lived as nomads: herders with no fixed home, who move with their animals after grass and water, as the Bedouin of Arabia did. Where there is water and soil, people farm, stay put and in time build towns.

Ibn Khaldūn, the fourteenth-century historian from Tunis, built a theory of history on this contrast. He called the hard life of the desert and the open country badawa, and the settled life of towns and cities hadara.

How far can such reasoning go? A century ago some geographers claimed that climate fixes a people’s character and worth outright. This view, environmental determinism, was used to excuse empire. It was abandoned, because the same land has carried very different societies. Arabia held herders for thousands of years and now holds cities of millions.

What the land gives is of two kinds. A renewable resource, such as sunlight, wind, timber or fish, is restored by nature as it is used, unless it is taken too fast. Coal, oil and gas are not. Once burned, they are gone.

What all may use and nobody owns is in danger. Each herder gains by adding one more animal to a shared pasture, and all share the damage, so it is grazed bare. This is the tragedy of the commons. Its cure is agreed limits. In early Islam a pasture could be reserved as a hima only for the public good.

Muslims have a further reason for care. The Qur’an says that God made human beings successors on the earth and tests them in what He has given them. Each generation succeeds the last, and the Arabic for such a successor is khalifa, which gave English caliph.