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# Area charts: Definition, differences and limits of these models

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## Area charts are invaluable tools for comparing data and their evolution over time. So what are they? What is the purpose of these charts? What are their limitations? And what about the different models? Find out the answers.

### What are area charts?

The area chart is used to compare quantitative data and show their evolution over time. To achieve this, the area chart combines line and bar charts. In this way, data are represented through several layers of different colors or textures (hatching, shading, etc.).

Although the area chart is often confused with the line chart, there are a few differences:

• The area below the line is colored. The aim is to indicate volume.
• The area chart is generally used to compare different data. Attributes are plotted on separate lines, and different colors are shown below each line.

Good to know: This mathematical model was developed by Scottish engineer and economist William Playfair in his book “The Commercial and Political Atlas”, published in 1786.

### What's it for?

The area chart is mainly used to show different trends over time.

But be careful, to provide analysts with an optimal representation. It is preferable to respect certain conditions:

• Data must be expressed as a total (the sum of each value must equal 100%);
• Data must be compared over time periods;
• The aim is to represent an overall trend, not individual values;
• There are several series of data with significant differences.

### What are the limits of the area chart?

While the area chart is particularly useful for representing global trends over time, it does suffer from a number of limitations. Indeed, if the above-mentioned conditions are not met, the area chart can be misleading and difficult to interpret.

We therefore advise against using it in the following situations:

• The aim is to show differences in values in a series of different categories: in this case, prefer the bar chart, column chart or split-bar chart.
• The total amount of data is small: choose a line chart.
The difference between values is small: again, choose a line chart.
• A single value is represented over time: line or column charts are more appropriate.
• The aim is to compare the size of different data: a line chart is preferable.

### What are the different types of area graphics?

Area charts can be divided into two sub-categories.

#### Graph of overlap zones

The idea is to compare values between different groups and highlight overlapping data.

Here’s an example: the area chart can show sales of Nokia, Blackberry, Samsung or iPhone. When certain brands experienced dizzying falls, other models were introduced. There are overlaps between the different lines. The graph highlights these overlaps, but also the sales peaks.

#### Stacked zone graph

Also known as a surface chart, this model aims to represent the total value of the data and its distribution within the dataset. The idea is to focus on volumes.

For example: in a store, managers can analyze the sales volume of products of brands X, Y and Z, and compare them over time.

### Things to remember :

1. The area chart can be used to compare several pieces of data and show their evolution over time.
2. While this model is effective for identifying temporal trends, it is not always the most relevant.
3. There are different types of area chart, with overlapping or stacked areas.

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