Customizing Maps in R: spplot() and latticeExtra functions

# setup environment
library(gstat)
library(latticeExtra)
library(grid)

# load example data
data(meuse.grid)
data(meuse)
data(meuse.alt)

# convert to SpatialPointsDataFrame
coordinates(meuse.grid) <- ~ x + y
coordinates(meuse) <- ~ x + y
coordinates(meuse.alt) <- ~ x + y

# converto SpatialPixelsDataFram
gridded(meuse.grid) <- TRUE

# convert 'soil' to factor and re-label
meuse.grid$soil <- factor(meuse.grid$soil, labels=c('A','B','C'))
meuse$soil <- factor(meuse$soil, levels=c('1','2','3'), labels=c('A','B','C'))


#
# example 1
#

# setup color scheme
cols <- brewer.pal(n=3, 'Set1')
p.pch <- c(2,3,4)

# generate list of trellis settings
tps <- list(regions=list(col=cols), superpose.polygon=list(col=cols), superpose.symbol=list(col='black', pch=p.pch))

# init list of overlays
spl <- list('sp.points', meuse, cex=0.75, pch=p.pch[meuse$soil], col='black')

# setup trellis options
trellis.par.set(tps)

# initial plot, missing key
p1 <- spplot(meuse.grid, 'soil', sp.layout=spl, colorkey=FALSE, col.regions=cols, cuts=length(cols)-1)

# add a key at the top + space for key
p1 <- update(p1, key=simpleKey(levels(meuse.grid$soil), points=FALSE, lines=FALSE, rect=TRUE, regions=TRUE, columns=3, title='Class', cex=0.75))

# add a key on the right + space for key
p1 <- update(p1, key=simpleKey(levels(meuse$soil), points=TRUE, columns=1, title='Class', cex=0.75, space='right', ))

p1




#
# example 2
#

# generate list of trellis settings
tps <- list(regions=custom.theme()$regions, superpose.symbol=list(col='black', pch=p.pch), fontsize=list(text=16))

trellis.par.set(tps)
p2 <- spplot(meuse.grid, 'dist', sp.layout=spl, colorkey=list(space='bottom', title='Distance'), scales=list(draw=TRUE, cex=0.5))

p2 <- update(p2, key=simpleKey(levels(meuse$soil), points=TRUE, columns=1, space='right'))

p2


#
# example 3
# more colorkey tweaking and...
# overlay 2 grids with layer()
#



sp.grid <- function (obj, col = 1, alpha = 1, ...)
{
    if (is.character(obj))
        obj = get(obj)
    xy = coordinates(obj)
    if (length(col) != 1 && length(col) != nrow(xy)) {
    }
    gt = as(getGridTopology(obj), "data.frame")
    grid.rect(x = xy[, 1], y = xy[, 2], width = gt$cellsize[1],
        height = gt$cellsize[2], default.units = "native", gp = gpar(fill = col, col = NA, alpha = alpha))
}



trellis.par.set(regions=custom.theme()$regions, superpose.polygon=list(col='black', alpha=0.25))

# first grid covers entire extent
p3 <- spplot(meuse.grid, 'dist', colorkey=list(space='bottom', width=1, height=0.5, tick.number=3))

# overlay partially transparent, kind of a hack...
p3 <- p3 + layer(sp.grid(meuse.grid[meuse.grid$soil == 'A', ], col='black', alpha=0.25))

p3 <- update(p3, key=simpleKey('Shaded Region', points=FALSE, lines=FALSE, rect=TRUE, columns=1, space='top'))

p3



#
# example 4: merge all three together
#

# order matters
p4 <- c(p3,p2,p1, layout=c(3,1))
p4 <- update(p4, key=simpleKey(levels(meuse$soil), points=TRUE, columns=1, space='right'))

p4


# save to file: note that we have to reset the 'regions' colors
png(file='spplot_examples.png', width=700, height=350)
trellis.par.set(regions=custom.theme()$regions)
print(p4)
dev.off()