R help - May 2011 - Overlaying maps

I'm having difficulty overlaying maps when writing to a file graphics
device. My command sequence has the structure

plot(map1)
par(new = T)
plot(map2)

On the screen device, it works fine. When I attempt something like

png(file = "map.png")
plot(map1)
par(new = T)
plot(map2)
dev.off()

only the last map appears, the previous ones having been cleared. Can
someone clarify?

Thanks,
Michael Laviolette PhD MPH
New Hampshire Department of Health and Human Services

Using my mind-reading skills, plot.Map(), while deprecated, does provide an add=
option.

If this doesn't help, you'll need to read the posting guide and provide
(a lot) more
information.

Ray Brownrigg

On Thu, 19 May 2011, Michael.Laviolette at dhhs.state.nh.us
wrote:
> I'm having difficulty overlaying maps when writing to a file graphics
> device. My command sequence has the structure
> 
> plot(map1)
> par(new = T)
> plot(map2)
> 
> On the screen device, it works fine. When I attempt something like
> 
> png(file = "map.png")
> plot(map1)
> par(new = T)
> plot(map2)
> dev.off()
> 
> only the last map appears, the previous ones having been cleared. Can
> someone clarify?
> 
> Thanks,
> Michael Laviolette PhD MPH
> New Hampshire Department of Health and Human Services
> 
> ______________________________________________
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> PLEASE do read the posting guide
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> minimal, self-contained, reproducible code.