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....@data[-c(22,69), 4]), 0), "kg/ha"),
col ="red", cex = 1)
# Scale bar limits and title
scmax <- round(max(md....@data[, 4]) / 50, 0) * 50
scmin <- round(min(md....@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....@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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