Discover the **population** structure

When you walk around in your municipality, you can meet people of very different ages: children younger than you, children your own age, but also older people, like your parents, or even older, like your grandparents.

Have you ever wondered how many people live in your municipality, how many children in your municipality are the same age as you, or what is the most common age of inhabitants or the average age? That’s what you will discover in this topic. And more.

Why don't you compare these proportions with those for Belgium, or with those you would get if you did the exercise on the pupils in your class? What would you find?

Imagine: we gather all the inhabitants of your municipality together in the school playground. We classify them in rows according to their age. We then count the number of inhabitants in each row and construct the chart below.

This chart is what is known as a bar chart or a bar graph (whichever you prefer), and is used to represent observations (in this case, the age of the inhabitants) according to their frequency (in this case, the number of inhabitants).

The longer the bar, the greater the frequency of the observation.

In a series of observations, the (absolute) frequency is the number of times a value is observed.

The observation with the highest frequency is called the mode.

Therefore, the most common age is the age that is most frequently observed, the age with the largest number of inhabitants.

When we talk about the average, we usually mean the arithmetic average.

To calculate the average age of the inhabitants of a geographical area, we need to:

1) add up the ages of all inhabitants of that area

2) divide this sum by the total number of inhabitants of that area.

The median is the central value of a series of observations.

The median is a value that divides the statistical series into 2, so that half of the observed values are lower and half of the observations are higher. The median may be one of the values observed in the series, but not always.

In order to determine the median, you first have to understand the concept of cumulative frequency.

Have fun comparing the populations with each other. Do the charts look alike? Are the most common ages the same? And the medians?

What conclusions can you draw?

**Choose another geographical area to compare.**

A population pyramid shows the distribution by gender and age of a given population at a given time.

It consists of 2 bar charts (one for each gender) with the number of inhabitants on the X-axis (horizontal axis) and the age on the Y-axis (vertical axis).

The population pyramid has the shape of a pyramid when there are many young people and few older people. You will see that this is not always the case.

You will see that a population pyramid does not always have the shape a pyramid. It can look like a bell jar, a mushroom, a spinning top, a tower, an urn or other shapes.

Your journey through the different municipalities of Belgium will undoubtedly make you discover other shapes.

This kind of chart allows us to compare populations with each other, but also to observe the effects of some historical facts on the population and to determine a trend on which politicians can base their decisions.

**Choose another geographical area to compare:**

Population density is a measure of the number of inhabitants occupying a given area, usually 1km². Density is not the same everywhere. Some places on earth are more densely populated than others per km².

You will see that in Belgium, population density is not the same everywhere. Some municipalities are more densely populated than others.

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