What does a Parallel Coordinate Plot do?

A: Parallel coordinates plot is a technique for representing high-dimensional data.

To show a set of points in an n-dimensional space, onto a 2D surface (ie. the computer screen), the graph is drawn consisting of n vertical, equally spaced parallel line segments.  The lines themselves are not visible in ioGAS, but have the sample points plotted as dots onto them, according to that sample’s value in that variable.  The number of vertical lines depends on the number of variables selected in the Select Variables Dialog.  Then the sample’s points on the various vertical lines are linked with a polyline.

Part of the value of parallel coordinates is that certain geometrical properties in high dimensions translate into easily seen 2D properties.  For example, a set of points that lie on a line in n-space will translate to a set of polylines in parallel coordinates that all intersect at a common point; two sets of points which occupy distinct spatial clusters will form ‘knots’ of lines that don’t intersect.

Selecting more variables and creating another PC plot is equivalent to adding more dimensions to the parallel coordinate plot.

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