[R-sig-Geo] spplot: 1) filling background polygon without overwriting foreground polygon; 2) left justifying sp.layout text

[Edzer Pebesma]

Thanks for the reproducable example. I can see what you want, and even
with the intended syntax, i.e.

sa.lst = list("sp.polygons", sa.shp, fill = "grey", first = T, col =
"black")

you don't get what I think you'd like. If the image attached is what you
want, I committed a code change to the sp repository. I want to run some
more checks to see whether it does not badly affect something else.

Best regards,

On 10/08/2010 04:18 PM, Lyndon Estes wrote:
> Greetings,
> 
> I have two questions related to spplot:
> 
> 1. I am trying to plot one SpatialPolygonsDataFrame over another, and
> fill the background polygon with grey. I can't seem to fill the
> background polygon without having it cover over my supposed foreground
> polygon, even if I specify "first = T" (which fails to draw the
> background polygon):
> 
> # Code
> 
> # Load shapefiles
> con1 <- url("http://sites.google.com/site/ldemisc/spplot-question/demo.mdshp.RData")
> con2 <- url("http://sites.google.com/site/ldemisc/spplot-question/demo.sashp.RData")
> load(con1); load(con2); close(con1); close(con2)
> 
> # Set up plot background shape and additional text for map
> 
> # Covers over md.shp
> #sa.lst = list("sp.polygons", sa.shp, fill = "grey", col = "black")
> 
> # Covers over md.shp
> #sa.lst = list("sp.polygons", sa.shp, fill = "grey", first = F, col =
> "black")
> 
> # sa.shp doesn't plot
> #sa.lst = list("sp.polygons", sa.shp, fill = "grey", first = T, col = "black")
> 
> # Background polygon works like this, but without fill
> sa.lst = list("sp.polygons", sa.shp, col = "black")
> 
> # Additional text - overall mean yield.
> text1 <- list("sp.text", c(360000, -3210000),
>              paste("Overall mean yield =",
> round(mean(md.shp at data[-c(22,69), 4]), 0), "kg/ha"),
>              col ="red", cex = 1)
> 
> # Scale bar limits and title
> scmax  <- round(max(md.shp at data[, 4]) / 50, 0) * 50
> scmin  <- round(min(md.shp at data[, 4]) / 50, 0) * 50
> byval  <- 25
> titlevec <- "Mean district maize yields (kg/ha) 1981-99: Cultivar PAN6528"
> 
> # Spplot
> dev.new()
> spplot(md.shp[-c(22,69),], z = 4,
>        sp.layout = list(sa.lst, text1),
>        col.regions = topo.colors(500),
>        at = seq(scmin, scmax, by = byval),
>        main = titlevec)
> 
> Any advice on how to correctly set "sa.lst" so that sa.shp fills
> underneath md.shp will be much appreciated.  I haven't been able to
> find a ready answer in the help files, except for this:
> 
> "The order of items in sp.layout matters; objects are drawn in the
> order they appear. Plot order and prevalence of sp.layout items: for
> points and lines, sp.layout items are drawn before the points (to
> allow for grids and polygons); for grids and polygons sp.layout is
> drawn afterwards (so the item will not be overdrawn by the grid and/or
> polygon). Although a matter of taste, transparency may help when
> combining things. "
> 
> But, beyond what I have tried so far, I can't figure out how to write
> the code so that sa.shp is drawn first.
> 
> The second question:
> 
> 2. Is there an option to pass to:
> 
> text1 <- list("sp.text", c(360000, -3210000),
>             paste("Overall mean yield =",
> round(mean(md.shp at data[-c(22,69), 4]), 0), "kg/ha"),
>             col ="red", cex = 1)
> 
> so that the text is left-justified on the coordinates  c(360000,
> -3210000)? At the moment it seems that the text is centered at this
> location.
> 
> Thanks in advance for any help you can provide.
> 
> Best, Lyndon
> 
> _______________________________________________
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-- 
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.pebesma at wwu.de
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