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Area Charts

Area charts are just like line charts, but with the space below the line filled in. This shading emphasizes the volume or magnitude of values over time.

Area charts answer the question, "How is this metric trending over time, and how much of it is there?"

When to Use Area Charts

Showing cumulative totals over time
Emphasizing the magnitude of change (not just direction)
Comparing multiple series that stack on top of each other

Secondary Y-Axis

Sometimes you want to compare two metrics that have very different scales. For example, session duration (in minutes) and pages visited (count) don't share the same range. A secondary Y-axis lets you plot both on the same chart without one metric squashing the other.

Use a secondary axis sparingly. If the two metrics aren't closely related, consider using two separate charts instead.

Assignment

Create a new page and name it Trends.
Insert an Area Chart spanning the top half of the page.
Configure the chart to show how the session_duration_minutes changes over the session_date.

Ensure the X-axis is not set to "Date Hierarchy" but to session_date. You can change this by clicking the down arrow on the session_date field in the X-axis well.
Add session_pages_visited to the Secondary Y-axis field to compare both metrics.
Format the title: General → Title → Text → "Session Duration & Pages Over Time"

Notice that the session durations and pages visited both seem to be on a slight downward trend... a marketer may care to know about that.

Save the project and, from the course directory, submit the CLI tests.