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# Glossary of Graphics Information

The following is a list of terms used in the graphing of data.

A, B. C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z

## A

• Aspect ratio: The aspect ratio of a graph is the height of the data rectangle divided by the width. An aspect ratio of 1 means the data rectangle is square with the height and width being the same length.

## B

• Bar chart: A bar chart is a chart with rectandular bars with lengths proportional to the values that they represent. The bars can be plotted vertically or horizontally. Bar charts are used for plotting discrete data.
• Boxplot: A boxplot is a graph of the statistical five number summary. A central box spans the the first (25th percentile) and third (75th percentile) quantiles. A line bisects the box at the median (50th percentile). Lines extend from the box to the smallest and largest observations. An alternate version of the box plot, the modified boxplot, has lines that extend from the box to 1.5 IQR (see below).

## D

• Dot Plot: A dot plot or dot chart is a statistical chart consisting of a group of data points plotted on a simple scale. Dot plots are used for continuous, quantitative, univariate data. For more information see: Wikipedia

## H

• Histograms: Histograms are used to represent the distribution of a single continuous variable. A histogram groups individual observations into bins (mouseover to define) of a specified (usually equal) width and counts the number of observations in each bin. Rectangles are drawn so that the height (or width for a horizontal histogram) represents the frequency, percentage, or density of the number of observations in each bin. By convention, the rectangles in a histogram touch one another. For more information on histograms see here.

## I

• IQR: The IQR (interquartile range) is the numerical difference between the third and first quartiles.

## J

• Jitter: Add a small amount of noise to a numeric vector.

## L

• Lattice: Lattice is a powerful and elegant high-level data visualization system in R, with an emphasis on multivariate data, that is sufficient for typical graphics needs, and is also flexible enough to handle most nonstandard requirements. See also Trellis (originating in the S Language).

## M

• Modified Box Plot: The modified box plot is similar to the box plot. However, lines from the box that spans the first and third quartiles extend to the data the smallest and largest observation within 1.5 IQR. Data points outside 1.5 IQR are shown as points on the graph.

## P

• Plotting Symbol: A plotting symbol, or plotting character, refers to the point, symbol, or letter on a graph representing a data point.

## Q

• Quartile: In descriptive statistics, a quartile is one of three points, that divide a data set into four equal groups, each representing a fourth of the distributed sampled population.

## S

• Scale: In graphics, the scale may have several meanings. One is the ruler along which the data is graphed. Another meaning corresponds to the number of data points included per a unit of measurement.

• Scatterplot: A scatterplot is a type of mathematical diagram using Cartesian coordinates to display values for two variable for a set of data. The data is displayed as a collection of points, each having the value of one variable determining the position on the horizontal axis and the value of the other variable determining the position on the vertical axis. This kind of plot is also called a scatter chart, scatter diagram and scatter graph. For more information see: Wikipedia

• Stem Plot: A stemplot (or stem-and-leaf plot), is a device for presenting quantitative data in a graphical format, similar to a histogram, to assist in visualizing the shape of a distribution. For more information on stem plots see Wikipedia

## T

• Tick Label: A tick label is the text information provided below the y- or x-axis to denote a specific value. A tick label is most often associated with a tick mark.
• Tick Mark: A tick mark is included on the y- and x-axis to denote a specific numerical value which is represented in the graph. A tick label may be provided below a tick mark to denote a value of the axis.
• Trellis: Trellis display is a framework for the visualization of multivariable databases, developed by W.S. Cleveland at Bell Labs in the 1990s. Its most prominent aspect is an overall visual design, reminiscent of a garden trelliswork, in which panels are laid out in rows, columns, and pages. On each panel of the trellis, a subset of the data is graphed by a display method such as a scatterplot, curveplot, boxplot, 3-D wireframe, normal quantile plot, or dotplot. Each panel shows the relationship of certain variables conditional on the values of other variables. A number of display methods employed in the visual design of Trellis display enable it to succeed in uncovering the structure of data even when the structure is quite complicated.
Trellis graphics is a trademark of Tibco Software Inc.
Reference:
R. A. Becker, W. S. Cleveland, M. J. Shyu (1996): The Design and Control of Trellis Display. Journal of Computational and Statistical Graphics, Vol. 5, 123-155

## Z

Topic revision: r7 - 17 Feb 2011 - 11:30:48 - AndreasKrause

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