Definitions

prognostic chart

Chart

[chahrt]

A chart or graph is a type of information graphic, that represents tabular numeric data and/or functions. It may also refer to any kind of diagram.

Overview

Charts are often used to make it easier to understand large quantities of data and the relationship between different parts of the data. Charts can usually be read more quickly than the raw data that they come from. 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 that presents percentages in different groups (such as "satisfied, not satisfied, unsure") are often displayed in a pie chart, but are more easily understood when presented in a horizontal bar chart . On the other hand, data that represents 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 of a chart

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 a chart is graphical, containing very little text, since humans are generally able to infer meaning from pictures quicker than from text.

One of the more important uses of text in a graph is in the title. A graph's title usually appears above the main graphic and provides a succinct description of what the data in the graph 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 respectively. 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 travelled (m)" is a typical x-axis label.

Within the graph a grid of lines may appear to aid in the visual alignment of data. The grid can be enhanced by visually emphasising the lines at regular or significant graduations. The emphasised lines are then called major grid lines and the rest of the grid lines are minor grid lines.

The data of a chart can appear in all manner of formats, with or without individual labels. It may appear as dots or shapes, connected or unconnected, and in any combination of colors and patterns. Inferences or points of interest can be overlayed directly on the graph to further aid information extraction.

When the data appearing in a chart contains multiple variables, the chart may include a legend. 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 of charts

Common charts

  • A histogram typically shows the quantity of points that fall within various numeric ranges (or bins).
  • A bar chart uses bars to show frequencies or values for different categories.
  • A line chart is a two-dimensional scatterplot of ordered observations where the observations are connected following their order.
  • A pie chart shows percentage values as a slice of a pie.
  • A scatterplot uses Cartesian coordinates to show the relation of two or more quantitative variables.
  • A timeline chart

Less-common charts

  • A box plot (or box-and-whiskers plot) shows information about the distribution (minimum, maximum, mean average, etc.) along a single axis.
  • A bubble chart is a two-dimensional scatterplot where a third variable is represented by the size of the points.
  • A doughnut chart
  • A Polar area diagram (developed by Florence Nightingale) is an enhanced form of pie chart.
  • A radar chart (or "spider chart") is a two-dimensional chart of three or more quantitative variables represented on axes starting from the same point.
  • A ternary plot is a barycentric plot on three variables which sum to a constant..
  • A waterfall chart also known as a "Walk" chart, is a special type of floating-column chart.

Field-Specific Charts

Some types of charts have specific uses in a certain field

  • Stock market prices are often depicted with a 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 minimise noise.
    • Alternatively, where less detail is required and chart size is paramount, a Sparkline may be used.
  • Interest rates, temperatures, etc., at the close of the period are plotted with a line chart.
  • Scatter charts plot readings of two variables simultaneously as dots between the X-axis and the Y-axis, such as for price and earnings.
  • Marketers use a lift chart to highlight performance.
  • Project planners use a Gantt chart to show the timing of tasks as they occur over time.
  • A phase diagram denotes the equilibrium conditions between thermodynamically-distinct phases.

Well-known (named) charts

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

Overview of charts by type

See also

References

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