Chart

For other uses, see Chart (disambiguation), Graph (disambiguation), and Diagram.

A pie chart showing the composition of the 38th Parliament of Canada

A chart (sometimes known as a graph) is a graphical representation for data and information visualization, in which "the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart". A chart can represent tabular numeric data, functions, or some kinds of qualitative structure.

The term "chart" as a graphical representation of data has multiple meanings:

• A data chart is a type of diagram or graph that organizes and represents a set of numerical or qualitative data.
• Maps that are adorned with extra information (map surround) for a specific purpose are often known as charts, such as a nautical chart or aeronautical chart, typically spread over several map sheets.
• Other domain-specific constructs are sometimes called charts, such as the chord chart in music notation or a record chart for album popularity.

Charts are often used to ease understanding of large quantities of data and the relationships between parts of the data. Charts can usually be read more quickly than the raw data. They are used in a wide variety of fields, and can be created by hand (often on graph paper) or by computer using a charting application. Certain types of charts are more useful for presenting a given data set than others. For example, data showing percentages in different groups (such as "satisfied, not satisfied, unsure") is often displayed in a pie chart, but may be more easily understood when presented in a horizontal bar chart. On the other hand, data representing numbers that change over a period of time (such as "annual revenue from 1990 to 2000") might be best shown as a line chart.

Features

A chart can take a large variety of forms. However, there are common features that provide the chart with its ability to extract meaning from data.

Typically the data in a chart is represented graphically, since humans can generally infer meaning from pictures more quickly than from text. Text is therefore usually used only to annotate the data.

One of the most important uses of text in a chart is the title. A chart's title usually appears above the main graphic and provides a succinct description of what the data in the chart refers to.

Dimensions in the data are often displayed on axes. If a horizontal and a vertical axis are used, they are usually referred to as the x-axis and y-axis. Each axis will have a scale, denoted by periodic graduations and usually accompanied by numerical or categorical indications. Each axis will typically also have a label displayed outside or beside it, briefly describing the dimension represented. If the scale is numerical, the label will often be suffixed with the unit of that scale in parentheses. For example, "Distance traveled (m)" is a typical x-axis label and would mean that the distance traveled, in units of meters, is related to the horizontal position of the data within the chart.

Within the chart, a grid of lines may appear to aid in the visual alignment of data. The grid can be enhanced by visually emphasizing the lines at regular or significant graduations. The emphasized lines are then called major gridlines, and the remainder are minor gridlines.

A chart's data can appear in all manner of formats and may include individual textual labels describing the datum associated with the indicated position in the chart. The data may appear as dots or shapes, connected or unconnected, and in any combination of colors and patterns. In addition, inferences or points of interest can be overlaid directly on the chart to further aid information extraction.

When the data appearing in a chart contains multiple variables, the chart may include a legend (also known as a key). A legend contains a list of the variables appearing in the chart and an example of their appearance. This information allows the data from each variable to be identified in the chart.

Types

Common charts

Among the most common types of charts are the histogram, the bar chart, the pie chart, and the line chart.

• 
  Histogram
• 
  Bar chart
• 
  Pie chart
• 
  Line chart

• A histogram consists of tabular frequencies, shown as adjacent rectangles, erected over discrete intervals (bins), with an area equal to the frequency of the observations in the interval. The term was introduced by Karl Pearson.
• A bar chart uses rectangular bars with lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. Early forms of the bar chart are usually attributed to Nicole Oresme, Joseph Priestley, and William Playfair.
• A pie chart shows percentage values as slices of a circle; it was introduced by William Playfair in 1801.
• A line chart is a two-dimensional scatterplot of ordered observations in which the observations are connected following their order. Early line charts are usually credited to Francis Hauksbee, Nicolaus Samuel Cruquius, Johann Heinrich Lambert, and William Playfair.

Other charts

Many other types of chart exist. Examples include:

• 
  Timeline chart
• 
  Organizational chart
• 
  Tree chart
• 
  Flow chart
• 
  Area chart
• 
  Cartogram
• 
  Pedigree chart
• 
  Radial tree

• 
  Bubble chart
• 
  Polar area diagram
• 
  Waterfall chart
• 
  Radar chart
• 
  Tree map
• 
  Streamgraph

• A bubble chart is a two-dimensional scatterplot in which a third variable is represented by the size of the points.
• A polar area diagram, sometimes called a coxcomb chart, is an enhanced form of pie chart popularized by Florence Nightingale.
• A radar chart, also called a spider chart, displays three or more quantitative variables on axes starting from the same point.
• A waterfall chart, also known as a "walk" chart, is a special type of floating-column chart.
• A tree map displays hierarchical data as nested rectangles whose areas correspond to values; additional dimensions can be represented with color or hue.
• A streamgraph is a stacked, curvilinear area graph displaced around a central axis.

Further examples include:

• 
  Control chart
• 
  Greninger chart
• 
  Heatmap
• 
  Natal chart
• 
  Nomogram
• 
  Pareto chart
• 
  Run chart
• 
  Strip chart
• 
  Structure chart
• 
  Vowel chart

Another example is the Bernal chart, used in X-ray crystallography.

Field-specific charts

Some types of charts have specific uses in a certain field. Several, for example, are used to depict stock market prices:

• 
  Open-high-low-close chart
• 
  Candlestick chart
• 
  Kagi chart
• 
  Sparkline

• Stock market prices are often depicted with an open-high-low-close chart, with a traditional bar chart of volume at the bottom.
• Candlestick charts are another type of bar chart used to describe price movements of an equity over time.
• A Kagi chart is a time-independent stock tracking chart that attempts to minimize noise.
• Where less detail is required and chart size is paramount, a sparkline may be used.

Other examples:

• Quantities such as interest rates and temperatures recorded at the close of each period are plotted with a line chart.
• Project planners use a Gantt chart to show the timing of tasks as they occur over time.

Well-known named charts

Some specific charts have become well known by effectively explaining a phenomenon or idea:

• 
  Gantt chart
• 
  Nolan chart
• 
  PERT chart
• 
  Smith chart

• A Gantt chart helps in scheduling complex projects.
• The Nolan chart and the Pournelle chart classify political philosophies according to two axes of variation.
• A PERT chart is often used in project management.
• A Punnett square is a grid used in genetics to show the possible combinations of parental alleles in offspring.
• The Smith chart serves in radio electronics.

Plots

Main article: Plot (graphics)

Frequently used statistical plots include the box plot, the dot plot, the probability plot, the scatter plot, and the biplot:

• 
  Box plot
• 
  Dot plot
• 
  Probability plot
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  Scatter plot
• 
  Biplot

Chart software

While charts can be drawn by hand, computer software is often used to automatically produce a chart based on entered data. For examples of commonly used software tools, see List of charting software.

See also

• Diagram
• Drakon-chart
• Edward Tufte
• Exploratory data analysis
• Graphic organizer
• Information graphics
• List of statistical charts and diagrams
• Mathematical diagram
• Misleading graph
• Official statistics
• Plot (graphics)
• Table (information)

Further reading

• Brinton, Willard Cope (1914). Graphic Methods for Presenting Facts. The Engineering Magazine Company.
• Karsten, Karl G. (1923). Charts and Graphs: An Introduction to Graphic Methods in the Control and Analysis of Statistics. Prentice-Hall.