[R] Adding a legend to a symbol plot

[Jennifer.Morin@colorado.edu]

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