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Diagrams Diagrams are an important

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tool for visualizing complex information

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in an understandable way, whether in

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school, scientific

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research, or business. They play

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a crucial role in the

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presentation of data and correlations.

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Line chart The line chart is

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a way of visually presenting data. It

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is used, for example, to show changes

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in values over time. This way

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you can identify certain developments or

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trends.

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But how do you actually create a

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line chart? A line chart

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basically consists of data points in

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a coordinate system. These points

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represent specific values at

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specific times. Most of the time

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time is on the x-axis and

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the value's height is on the y-axis. All of these

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data points are then connected by a line.

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to each other.

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To understand this better, let's look

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at the example of

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average daily temperatures in

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March. This table records

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the temperature on each day in March.

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Each row of the table is

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a data point. We see the date — that is,

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the point in time — and the temperature —

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the value. But many data points can

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quickly become confusing. To make them

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clearer, we draw

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a coordinate system. As before, time is

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on the x-axis and the value

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on the y-axis. Now we can

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read the time and value for each data point

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from the table and enter them

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into the coordinate system. The points

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alone often still look

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confusing, which is why the points

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are connected with a line. That’s

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where the name "line chart" comes from.

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The line improves readability and

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clarity of the diagram. You can

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especially see this when comparing

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charts with and without lines.

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From our line chart, we can

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now tell, for example, that March 14th

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was significantly warmer than

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the other days. On March 21st, it

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was the coldest. We can also

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see that the temperature rose

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rapidly here and only slightly

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there. But overall, we can say that

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between March 21st and 23rd

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it got warmer. This kind of change

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in a value over time — when something

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increases or decreases over a period —

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is called a trend. Between

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March 21st and 23rd we thus see

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an upward trend. Depending on the data,

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values can even fall into negative

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ranges. In a temperature chart, for example,

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it could be that in cold

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winter months, temperatures drop below zero.

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In such cases, the diagram

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can simply be extended downward.

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So, now you know what a line chart is  

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and how it’s created. But when is a line chart  

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the right type of chart to use?  

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A line chart is always helpful  

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when you want to display a trend  

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over time. That is, when a value  

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increases or decreases  

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over a certain time span.  

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It’s important that the data is continuous.  

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This means that a relationship exists between the  

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data points. For example, the average  

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daily temperature.  

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Here, you would not expect  

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a sudden jump, but rather a gradual change.  

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In that case, the line connecting the dots  

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makes sense and helps  

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make the course of the data more clear.  

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A line chart can also be used  

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to compare multiple developments  

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at the same time.  

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To do that, simply draw more  

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lines in the same diagram —  

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one for each dataset.  

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In the end, let’s summarize again:  

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A line chart shows how  

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a value changes over time.  

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Data points are entered into a coordinate system  

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and connected with lines.  

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This makes trends and patterns  

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easier to recognize.  

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The line chart is especially helpful  

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when the data changes gradually  

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and the values are continuous.  

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That's how a line chart works!
-------------------

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With a line, you can now

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easily compare the different CO2 emissions

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across different world regions.

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For example, we see that

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Australia, North America, and Europe

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emit much more CO2 than Asia,

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South America, and Africa. Also, you can

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immediately see the changes

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in CO2 emissions in all world regions

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over time — that’s what we call

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global trends.

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Area chart.

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Besides the line chart, there's also

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the area chart.

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At first glance, the two look very similar,

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but there is one

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important difference: in the

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area chart, the values are

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stacked on top of each other. This way, you see

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how different categories contribute to

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a total value — something you

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don't see in a line chart.

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Let’s look at an example

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of this area chart and the data

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it’s based on.

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Here we see sales numbers for

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products. In January, for example, 50 units

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of Product A, 30 units of Product B, and

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20 units of Product C were sold —

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100 units in total across all

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products combined.

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In an area chart, you plot

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the points like this:

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The line for Product C — the red one —

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starts here at 100, even though in the

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table we see only 20 units were sold.

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That’s because the 20 units of Product C

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are stacked on top of the 30 units

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of Product B, which are in turn stacked

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on top of the 50 units of

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Product A.

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So the values are added together.

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The final chart looks like this.

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Now let’s compare the area chart

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with a line chart that uses the same data.

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That would look like this:

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You can see that in a line chart, values are

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not added together, i.e.

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not stacked. In the

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line chart, the red line

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for Product C actually starts at 20,

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the orange line for Product B at 30,

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and the green line for Product A at 50.

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But if you can already see that in the

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line chart — why use an

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area chart at all?

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Area charts always show

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the various categories as part

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of a whole. In an area chart,

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you can instantly see that in July,

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220 units of all products were sold.

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That’s something you can’t see

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in a line chart.

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However, in the area chart, you only see

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roughly that of these 220 units,

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most were Product A and the fewest were

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Product C. In the line chart,

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you don't see the 220 units — but you do see

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the exact values: 110 from

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Product A, 60 from Product B, and 50 from

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Product C.

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To get the exact values from the area chart,

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you'd have to do a little math and subtract

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individual values from the total.

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Let’s take another example with

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CO2 emissions — this time about emissions

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in Austria caused by burning different

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types of fuels. An area chart

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clearly shows how

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total emissions have developed.

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You notice that oil usage

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has steadily increased since the 1960s.

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Between 2000 and 2010,

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coal use dropped significantly.

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At the same time, you also see peak values

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in total emissions.

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In summary: line charts

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show precise differences between emissions

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from gas, coal, and oil,

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while area charts better show

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the total values.

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Streamgraph.

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A streamgraph is very similar

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to an area chart. You can see the total value

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and how much each category contributes

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to that total.

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However, the values are not plotted

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in a coordinate system — instead, they're arranged

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around a central axis.

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This makes the streamgraph look

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a bit like waves in a river —

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or “stream” in English.

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Here’s a streamgraph, for example, that shows

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how many products from five different categories

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were sold throughout the year.

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The x-axis shows the time,

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and the colored waves show

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how much of each product was sold.

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You can see that between March and April

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and between August and September,

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almost no Product B was sold.

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But you can't read the exact total values,

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only the general trends,

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because area division in a streamgraph

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is very complex. Drawing one by hand

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would be quite difficult, so streamgraphs are usually

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generated by computer — because the computer

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processes data correctly and arranges the

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areas in a way that looks nice.
