Change over time can be expressed using a time series chart, which is a chart that represents data points in chronological order. Charts that express change over time include: line charts, bar charts, and area charts.

Showing change over time

Both bar charts and pie charts can be used to show proportion, which expresses a partial value in comparison to a total value.

Bar charts express quantities through a bar’s length, using a common baseline
Pie charts express portions of a whole, using arcs or angles within a circle
Bar charts, line charts, and stacked area charts are more effective at showing change over time than pie charts. Because all three of these charts share the same baseline of possible values, it’s easier to compare value differences based on bar length.

Bar and pie charts


Area charts come in several varieties, including stacked area charts and overlapped area charts:

Stacked area charts show multiple time series (over the same time period) stacked on top of one another
Overlapped area charts show multiple time series (over the same time period) overlapping one another
Overlapping area charts are not recommended with more than two time series, as doing so can obscure the data. Instead, use a stacked area chart to compare multiple values over a time interval (with time represented on the horizontal axis).

Area charts

Multiple types of charts can be suitable for depicting data. Guidelines provide insight into how to choose one chart over another.

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- Change over time
- Category comparison
- Ranking
- Part-to-whole
- Correlation
- Distribution
- Flow
- Relationship

Types of Charts

Part-to-whole charts show how partial elements add up to a total.

Use cases include:

Consolidated revenue of product categories
Budgets

Part-to-whole

Flow charts show the movement of data between multiple states.

Use cases include:

- Fund transfers
- Vote counts 
- Election results

Flow Charts

Change over time charts show data over a period of time, such as trends or comparisons across multiple categories.

Common use cases include:

- Stock price performance
- Health statistics
- Chronologies

Change Over Time Charts

Category comparison charts compare data between multiple distinct categories.

Use cases include:

- Income across different countries
- Popular venue times
- Team allocations

Category Comparison Charts 

Correlation charts show correlation between two or more variables.

Use cases include:

Income and life expectancy

Correlation Charts

Selecting Charts

Ranking charts show an item’s position in an ordered list. Common use cases include election results and performance statistics.

Ranking Charts

Relationship charts show how multiple items relate to one another. Use cases include mapping social networks and creating word charts.

Relationship Charts

Distribution charts show how often each value occurs in a dataset. Use cases include: population distribution, income distribution.

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