A line chart illustrates trends over time or plots the relationship between two or more variables.

In line charts showing trends, the vertical, or y, axis shows the amount, and the horizontal, or x, axis shows the time or other quantity against which the amount is being measured.

Both axes often start at zero in the lower-left corner, but you can exercise a fair amount of flexibility with both axes in order to present your data as clearly as possible.

When comparing two or more sets of data, you can plot them on the same chart for instant visual comparison.

Because they often show trends based on historical data, line charts often prompt questions about what comes next. Regression analysis can extend historical trendlines into the future, but these techniques must be used with care.

A surface chart, also called an area chart, is a form of a line chart with a cumulative effect; all the lines add up to the top line, which represents the total.

This presentation helps illustrate changes in the composition of something over time.

A bar chart portrays numbers by the height or length of its rectangular bars, making a series of numbers easy to read or understand.

Vertical bar charts are sometimes called column charts.

Bar charts are particularly valuable when you want to

• Compare the sizes of several items at one time.
• Show changes in one item over time.
• Indicate the composition of several items over time.
• Show the relative sizes of components of a whole.

Bar charts can appear in various forms:

• Grouped bar charts compare more than one set of data, using a different colour or pattern for each set.
• Deviation bar charts identify positive and negative values, or winners and losers.
• Segmented bar charts, also known as stacked bar charts, show how individual components contribute to a total number, using a different colour or pattern for each component.
• Combination bar and line charts compare quantities that require different intervals.
• Paired bar charts show the correlations between two items.

A chart that portrays data as symbols instead of words or numbers is known as a pictogram.

A timeline chart uses bars to show how much time is needed to complete each task in a given project; the specialized form known as a Gantt chart is often to track the progress of projects.

Scatter or XY diagrams compare entities against two variables.

Bubble diagrams compare them against three, with the size of the bubble representing the third variable.

A pie chart is a commonly used tool for showing how the parts of a whole are distributed.

Pie charts are indeed common, but in many instances, they are not as helpful to readers as bar charts, tables, and other types of visuals.

Conventional charts and graphs are limited in several ways:

• Most types can show only a limited number of data points before becoming too cluttered to interpret
• They often can’t show complex relationships among data points
• They can represent only numeric data.

A diverse class of display capabilities known as data visualization work to overcome all these drawbacks.

Unlike charts and graphs, data visualization is less about clarifying individual data points and more about extracting broad meaning from giant masses of data or putting the data in context.

In addition to displaying large data sets and linkages within data sets, other kinds of visualization tools combine data with textual information to communicate complex or dynamic data much faster than conventional presentations can.