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This is Suzanne. Her job is to plan what kinds of buildings should be built in the city where

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she lives. She works as a city planner. Suzanne is inspecting a plot the city has bought.

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But what should be built? The city's inhabitants are of different opinions. Jenny dreams of

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living in a big house for young people when she's old enough to leave home. There needs

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to be a rehearsal studio. John wants a new school to be built on the plot Suzanne is inspecting,

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then his children won't need to travel so far in the mornings. And Cecilia thinks that there

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is a shortage of apartments that suit the needs of the elderly. There's a need for a house with

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an elevator and a garden. All ideas are possible to carry out, but planning a construction project

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takes time. It can take many years to get all the decisions in place and until a building is

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finished. By then Jenny will be a grown-up woman. John's children will have left school

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and Cecilia, well, she might not even be alive. To make a decision, Suzanne needs to learn more

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about the city's inhabitants. Not only those who live in the city right now, but also about those

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who will live there in the future. Suzanne needs the help of demography. The word demography comes

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from Greek. Demos means people and grafo means description. Demography is what we use when we

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want to describe a population. And for that, we need facts and figures. We need statistics.

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In most countries, government agencies collect information about the people who live there.

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The number of births, the number of deaths, how many move in and out of the country,

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where people live, their address, how many are studying, are unemployed, have jobs,

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their occupations, and much more.

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All this information is saved in registries.

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But it takes a lot of effort to construct accurate registries.

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In poor countries with many inhabitants,

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or countries where there's war, statistics are often missing.

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To learn more about the population, a state can conduct a census.

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In the world's most populous country, China, a census was conducted in 2010.

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Six million people made calls or knocked on doors to ask questions about each household,

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how many people live at the address, how old they are, what gender they are, and about their level of education.

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When the census was finished, they had counted 1.37 billion people.

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Oh, right, we were supposed to help you.

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In the city where Suzanne works, accurate registries have been kept for a long time.

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That means we know quite a lot about those who live in the city right now,

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and about those who've lived there in the past.

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With the help of these statistics, we can try to predict who will live in the city in the future.

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We can make a forecast.

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When we make forecasts, we look at statistics and try to see patterns.

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We try to understand how what has happened in the past might influence what will happen in the future.

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That is what we need to do now.

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In the registries, we find statistics from the last few years.

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Every year fewer and fewer children are born

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Most young people move away from the city after leaving school

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And the retired in this city people live to become very old

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Most of those who move to the city from other places are also retired people

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Now we can make a forecast

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Are you with us, Suzanne?

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Not many children are being born

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that means there'll be no need for more schools in the future.

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Many young people leave.

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This means a big house for young people would probably not be fully used.

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We know that people grow very old

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and that retired people continue to move into the city.

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This means that the number of elderly people will grow

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while the proportions of children and young people will go down.

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The city has an ageing population.

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In the future, there'll be a need for housing that suits the needs of elderly people.

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So, Suzanne will plan for more buildings with lifts and gardens.

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And maybe a studio too.