Dear list, I've noticed a width/height scaling bug in multi-panel plots when you change the active plot using par mfg The underlying par setting that maps the full plot width (or height) to the numerical axis labels does not get updated when you change plots with par(mfg=...). Thus plotting a point at c(10,10) in the first plot will only be in the correct place IF the most recently generated plot had the same x and y limits. This affects all plots except the most recently created one. The error is reproduced whether you set the plot up using: par(mfcol=c(1,3)) -or- par(mfrow=c(1,3)) -or- layout(matrix(c(1,3),1,2)) I've tested this with 2x2, 1x2, 1x3 plots and all reproduce the error Tested on R 2.8.0 on OSX and R 2.7.1 on WinXP and both reproduce the error See ### comments for the errors below. cheers, Mark # draw 3 simple plots par(mfcol=c(1,3)) plot(1:100, 1:100) plot(1:200, 1:200) plot(1:300, 1:300) # add points to first plot which should span the whole plot par(mfg=c(1,1)) points(1:100, 1:100, pch="x", col="red") # you should only see one dotted line at 100 abline(v=c(100,200,300), h=c(100,200,300), lty=c("dotted", "dashed", "solid")) ### instead you see 3 lines at 33, 66, 100 # add points to second plot which should span the whole plot par(mfg=c(1,2)) points(1:200, 1:200, pch="x", col="red") # you should see a dotted and dashed line at 100 and 200 abline(v=c(100,200,300), h=c(100,200,300), lty=c("dotted", "dashed", "solid")) ### instead you see 3 lines at 66, 133, 200 # add points to third plot which should span the whole plot par(mfg=c(1,3)) points(1:300, 1:300, pch="x", col="red") abline(v=c(100,200,300), h=c(100,200,300), lty=c("dotted", "dashed", "solid")) ### there are indeed 3 lines at 100, 200, 300 sessionInfo() R version 2.8.0 (2008-10-20) i386-apple-darwin8.11.1 locale: en_AU.UTF-8/en_AU.UTF-8/C/C/en_AU.UTF-8/en_AU.UTF-8 attached base packages: [1] graphics grDevices datasets utils stats methods base other attached packages: [1] pwbc_0.1 mjcdev_0.1 tigrmev_0.1 slfa_0.1 sage_0.1 [6] qtlreaper_0.1 pajek_0.1 mjcstats_0.1 mjcspot_0.1 mjcgraphics_0.1 [11] mjcaffy_0.1 haselst_0.1 geomi_0.1 geo_0.1 genomics_0.1 [16] cor_0.1 bootstrap_0.1 blat_0.1 bitops_1.0-4 mjcbase_0.1 [21] gdata_2.4.2 gtools_2.5.0 ----------------------------------------------------- Mark Cowley, PhD Peter Wills Bioinformatics Centre Garvan Institute of Medical Research, Sydney, Australia