[R-sig-Geo] Kernel density plot on a US map

Ashton Shortridge ashton at msu.edu
Tue Mar 22 16:05:07 CET 2011

Hi Ravi,

> generating the kernel density plots but unable to superimpose the density
> plot on the US map???
Check out the following R code. 


# Make a random set of lat-lon pairs with values
usdat <- data.frame(x=runif(50, -115, -85), y=runif(50, 33, 41), z=runif(50, 
0, 100))

points(usdat$x, usdat$y)  # do they fall in there?

# Create an owin object from the USA outline(s)
usmap <- map('usa', fill=TRUE, col="transparent", plot=FALSE)
uspoly <- map2SpatialPolygons(usmap, IDs=usmap$names, 
proj4string=CRS("+proj=longlat +datum=wgs84"))
usowin <- as.owin.SpatialPolygons(uspoly)

# Create a spatstat ppp object
pts <- as.ppp(usdat, W=usowin)

# Plot a a density surface

# Plot a smoothed surface using the weights
plot(smooth.ppp(pts, 3))

On 2011-03-22, vioravis, wrote:
> I am trying to plot the kernel density plot superimposed on a US map. The
> data consists of the the latitude and the longitude of a few locations in
> the US and a number (such  as count) corresponding to each location. I
> would like to generate a kernel density plot with the count as the
> variable superimposed on US map so that I can visualize how the count
> varies across the US. I have looked at packages such as spatstat about
> generating the kernel density plots but unable to superimpose the density
> plot on the US map???
> Can someone help me on how to do this in R?
> Thank you.
> Ravi
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Ashton Shortridge
Associate Professor			ashton at msu.edu
Dept of Geography			http://www.msu.edu/~ashton
235 Geography Building		ph (517) 432-3561
Michigan State University		fx (517) 432-1671

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