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5. Line and Area Charts
Line charts and area charts are commonly used in Power BI for tracking trends, especially over time. We’ll learn how to use them in this lesson.
- The line chart displays data as one or more lines connecting a series of data points
- It is commonly used when you want to analyze trends over time
- If you are more interested in numeric amounts, another chart type may make more sense
- An area chart is a line chart with the area underneath the line highlighted
- Be aware that this can cause confusion if the bottom of the y-axis is not zero
Stacked Area Chart
- An area chart with multiple lines can be difficult to interpret, due to overlapping areas
- The stacked area chart stacks each area on top of each other
- The disadvantage is that it can be more difficult to compare the different areas at a particular time
In this lesson, we'll continue our assessment of the different chart types in Power BI, focusing on Line and Area charts.
We'll start by looking at Line charts.
The Line chart is another chart that's frequently used in reports and dashboards.
These charts are most commonly used to analyze the trend and the variable over time.
Let's say we want to analyze the number of customers by month. We want to get an idea of whether there are more or fewer transactions at certain times of the year.
Before we bring our data onto the canvas, we'll select a Line chart from the Visualizations pane creating a blank Line chart.
We'll then drag the Date field to the Axis well and the Company Name field to the Values well. By default, the Date field comes as a hierarchy of year, quarter, month, and day. We'll discuss this in greater detail in later lessons, but for now, we're only concerned with the number of companies by month. As such, we'll get rid of year, quarter, and day by selecting the Xs next to them.
We can see that the number of customers varies by month and seems to drop off considerably towards the end of the year. Let's modify this graph by adding the Region field as a legend.
We now have four different lines, one for each Region.
Let's move on and look at Area charts.
Area charts are similar to Line charts, however the area underneath each line is shaded.
We'll convert our Line chart to an Area chart by selecting the appropriate button in the Visualizations pane.
In theory, this should make it easier to see the changes in magnitude of each line. But with four lines on our chart, it's a bit unclear.
Let's take a Legend out again, and go back to a single line.
The Area chart now works quite well. The variations in data are much easier to see then with a simple Line chart.
Note that the bottom of the y-axis is not zero on Line and Area charts.
So while December is smaller then all other months, it's not as close to zero as you might think.
Line charts generally focus on trends over time, so the amount at any given point is less important.
However, with an Area chart, people may instinctively expect the y-axis to start from zero.
If you think viewers may be confused by this, you can either modify the axis values in the Format section of the Visualizations pane or use another visual like a Bar chart.
Let's add the Region legend back to the chart.
As we mentioned before, this is not the best visual. This is partly because it's difficult to separate the four areas and partly because two of our lines, the northeast and south regions, cross each other several times.
To address these issues, let's switch to a Stacked Area chart.
The areas are now stacked on top of each other rather then overlapping as they did on the previous graph.
The number of customers in each region is indicated by the size of the relevant area for any specific month.
For example, while the west region is on top of the chart, it consistently has the smallest area indicating the fewest customers.
As we can see, when we have multiple lines or lines that cross over each other, the Stacked Area chart is much easier to read.
Let's stop the lesson here. As one can imagine, both Line and Area charts are heavily used in time intelligence, something we'll cover in later courses. In the next lesson, we'll look at combining Line and Bar charts into a single insightful graph.