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bivariate proportional symbol map

September 17 2008 | 0 comments
Categories: Cartographic Design, Symbology

I tried creating a bi-variate proportional symbol map where circle size was one variable and a three class color fill of the circles the second variable. The software would allow me to create a graduated circle bi-variate map but not a proportional circle. Why?

Am I missing something?

Mapping Center Answer:

You're not missing anything--the user interface for the bivariate symbology method was designed to show categories by graduated color or symbol.

It's possible to achieve the effect of categories by proportional symbol by classifying the graduated attribute with a relatively large number of classes.  The trick is to set the number of classes to be at least 2x the symbol size range (so there will be no greater than a 0.5 point difference in symbol size differences, creating the effect of a visually smooth transition that cannot effectively be measured; so for a printed map I would 4x -6x). I would also suggest using the Defined interval classification to set up the breaks, rather than the default of Natural Breaks (Jenks).


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