[R] Adding a legend to a symbol plot

[Berton Gunter]

Not an answer, but a note. Encoding the mean temperature as the circle
radius is a bad idea: the eye perceives the area and so the radius^2, thus
the perceived effect is the square of the actual temperature effect (Howard
Wainer once referrred to this as "goosing up the effect by squaring the
eyeball.") . You should encode the sqrt of the temperature as the radius so
that the area is proportional to temperature. Details matter in graphical
perception.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> Jennifer.Morin at colorado.edu
> Sent: Thursday, June 02, 2005 11:57 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Adding a legend to a symbol plot
> 
> I have created a symbol plot with circles that represent the 
> mean temperature
> at lat/lon locations over the United States. The radius of the circle
> corresponds to the mean temperature. I would like to add a legend that
> identifies a range of temperatures (e.g. 0-10, 10-20, etc) 
> with circles of the
> appropriate radii next to them. I've read the manual on how 
> to add a legend,
> and I'm fine with adding one to the plot. However, I cannot 
> get circles of
> different sizes to come up next to the ranges in my legend. 
> All that is coming
> up are circles of all the same radius. In looking at the R 
> manual, it appears
> that in order to get the right radius for the circles, I have 
> to use the "pch"
> parameter in the "legend" command, but I'm unclear on how I 
> should define this
> parameter. Can anyone help?
> 
> thanks,
> Jennifer Morin
> 
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