by Mike Mueller

Created on: June 02, 2009

The purpose of a graph is to visually depict a set of data in a manner that all of the data can be viewed simultaneously and quickly processed by the interpreter. A graph is typically presented on a two dimensional medium and therefore the simplest graphs to interpret that require the least specialized training for both the presenter and the viewer are also constructed in two dimensions. Some graphs may be three dimensional, such as stereo nets, but do to the complexity of providing a graphing system of three dimensions on two dimensional portable medium, special training is required to produce and interpret such a graph so these communications are typically not as widely distributed as the much more universally applied two dimensional graphs.

A two dimensional graph is typically constructed on a pair of perpendicular axes, one oriented in the vertical direction, the other oriented in the horizontal direction; which correspond to the Cartesian coordinate system as the 'y-axis' and the 'x-axis', respectively. Where the two axes intersect is referred to as 'the origin' of a Cartesian plane. The Cartesian convention allows for negative values to left and to the downward side of the origin along these two axes and absolute or positive values to the right and vertically upward of the origin.

Thus data from a set of data in a table, or functional values from mathematical formula's render well on a Cartesian system. A visual survey of all the data simultaneously plotted on a Cartesian plane allows the viewer to detect patterns, trends, anomalies, and other data and functional characteristics in this presentation that would be less recognizable if it were presented as a list or in table format. It is for this reason that line graphs and bar graphs are a popular medium for portraying raw data stored in tables.

A bar graph positions each record along the horizontal axis according to criteria that is depicted as a label on the axis. The positioning of data in the horizontal denotes a sorting order. For example, the time stamp of the record might be used to determine the records position on the horizontal dimension and then that axis would be labeled as 'time' or 'date'. If temporal positioning is being graphed, it will almost always be depicted in the horizontal, as per convention. The spacing of data on a bra graph is typically at discreet points along the axis and the display is typically not proportioned, but there are occasional exceptions.

The vertical

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