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#### A.4.5.15 Contour Form

The Contour form () plots position density contours. These provide another way (alongside the Auto, Density and Weighted shading modes) to visualise the characteristics of overdense regions in a crowded plot.

The contours are currently drawn as pixels rather than lines, so they don't look very beautiful in exported vector output formats (PDF, PostScript).

Example Contour plot

Contour form configuration panel

The configuration options are:

Level Count
  The number of contours drawn. In fact this is an upper limit; if there is not enough variation in the plot's density, then fewer contour lines will be drawn.
Smoothing
  The size of the smoothing kernel applied to the density before performing the contour determination. If set too low the contours will be too crinkly, and if too high they will lose definition.
Scaling
  How the smoothed density is treated before the contours levels are determined. Options are linear, logarithmic and equal area.
Zero Point
  Determines the level at which the first contour (and hence all the others, which are separated from it by a fixed amount) are drawn. By sliding this from side to side you can sweep the contours over the density range and get a good idea of where interesting features lie.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk