Edzer, I think you've done the right thing -- and thank you for the quick response.
Ironically, in the application that brought this up plotting higher values on top was convenient, because higher values are of more interest. However, I can still have higher values on top simply by sorting before plotting. The user now has more control, and this is good. -Don -- Don MacQueen Lawrence Livermore National Laboratory 7000 East Ave., L-627 Livermore, CA 94550 925-423-1062 On 3/5/12 5:40 AM, "Edzer Pebesma" <edzer.pebe...@uni-muenster.de> wrote: >This has now been changed/repared in sp on r-forge (svn), and will >appear from sp 0.9-97 on. A test run would be: > >library(sp) >xyz = data.frame(expand.grid(x=1:10,y=1:10),rnorm(100)) >coordinates(xyz)=~x+y >spplot(xyz, cex=10) > >which used to plot points in value order, and does now in data record >order. > >I put up resulting graphs, for comparison, at >http://ifgi.uni-muenster.de/~epebe_01/xyz.html > >As this change may make some of your spplot's for points different, if >there are objections against this change (which I consider an >improvement, if not a bug fix), it is time now to let me / us know. > >On 03/02/2012 09:03 PM, MacQueen, Don wrote: >> I have a SpatialPointsDataFrame object in which many points are very >>close >> together, such that the markers (plotting characters) tend to overlap. >>(Of >> course, this depends on marker size and the scale at which I plot; if I >> "zoom in" there is less overlap.) >> >> It appears that when markers overlap, spplot() places a marker >>associated >> with the larger value after, and therefore on top of, a marker >>associated >> with a smaller value. >> >> Am I correct? Or more generally, what is the algorithm that determines >>the >> order in which markers are added? >> >> >> I have searched ?spplot and related help pages and haven't found an >> explanation (at least, not yet). >> >> I can add that I don't believe markers are placed in the order in which >> they appear in the SpatialPointsDataFrame. I say this because when I >> attempt to reproduce an spplot using base graphics plot() I have to sort >> from smallest to largest value to succeed. >> >> I can probably provide a small reproducible example if necessary, but >>I'm >> hoping it's not necessary. >> >> Here are my actual commands. >> >> tmps is the SpatialPointsDataFrame. >> tmp is coordinates(tmps) >> (they have the same number of rows in the same order) >> >> Note that I'm using the cuts argument to break a continuous variable >> ('cpm2') into bins. I have carefully matched the colors in tmps$col2 >>with >> the cbin.cols object passed to spplot(), and the break points for the >>bin >> boundaries, so I believe that everything else that could affect the >>final >> appearance, other than the order in which the markers are placed, is >> controlled. >> >> #1 using spplot >> spplot(tmps,c('cpm2'), >> key.space='right', >> legendEntries=cbin.lbls, >> cuts=cbin.brks, >> col.regions=cbin.cols, >> cex=0.4) >> >> #2 using base graphics >> plot(tmp[,1],tmp[,2], asp=1, cex=0.6, pch=16, col=tmps$col2) >> >> >> >> Thanks >> -Don >> > >-- >Edzer Pebesma >Institute for Geoinformatics (ifgi), University of Münster >Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251 >8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de >http://www.52north.org/geostatistics e.pebe...@wwu.de > >_______________________________________________ >R-sig-Geo mailing list >R-sig-Geo@r-project.org >https://stat.ethz.ch/mailman/listinfo/r-sig-geo _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo