Hi Enrico, I have some code to do map generalisation (reducing map resolution without visible loss in detail) at http://github.com/hadley/data-counties/tree/master. It's applied to counties data, but would be trivial (if slow) to modify to work with zip codes instead
Hadley On Sun, Apr 26, 2009 at 3:06 PM, Enrico Rossi <enrico.a.ro...@gmail.com> wrote: > Hello, > > I have some data at the zip code level, and I'm using the shapefiles > downloaded from the Census TigerLine website > (http://www2.census.gov/geo/tiger/TIGER2008/tl_2008_us_zcta5.zip) to > plot a shaded map of the US. However, the files generated in this way > are enormous, and take a long time to process, even on a fast machine > with lots of memory. I'm wondering if there's a more efficient way to > do this. Maybe rasterize before plotting somehow? > > If anyone on this list has experience working with zip-level data, I'd > appreciate any advice. > > Here's some example code like what I'm doing: > > # This works, and produces a 1.2GB PDF file! After it's done, I can > rasterize it using gs to reduce file size, but it takes almost an hour > library(maptools) > zip<-readShapePoly("tl_2008_us_zcta5") # This takes a while! > val<-runif(length(zip[[1]])) # there are about 32000 zip codes > pdf("zipplot.pdf") > plot(zip,xlim=c(-130,-65),ylim=c(20,50),col=grey(val),lty=0) > dev.off() > system("gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=png16m -r300 > -dTextAlphaBits=4 -dGraphicsAlphaBits=4 -dMaxStripSize=8192 > -sOutputFile=zipplot.png zipplot.pdf") > > # I've tried plotting directly to png, but it just seems to hang, my > patience ran out after two hours > png("zipplot.png") > plot(zip,xlim=c(-130,-65),ylim=c(20,50),col=grey(val),lty=0) > dev.off() > > # This also takes too long, I never got any output out of it > library(lattice) > zip$val<-val > pdf("zipplot2.pdf") > spplot(zip,"val",xlim=c(-130,-65),ylim=c(20,50),lty=0) > dev.off() > > Many thanks! > Enrico Rossi > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > -- http://had.co.nz/ _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
