[R] SpatialPolygon with the max value gets no color assigned in spplot function when using

[Roger Bivand]

Jan Hornych <jh.hornych <at> gmail.com> writes:

> 
> Hi,
> 
> I would like to do coloring of map regions based on the region values
> "weight". The approach I am taking is first to break regions into
> equal intervals,
> 
> classIntervals(spdf$weight,4)$brks #4 intervals in this case
> 
> and coloring all regions within the interval with the same color
> 
> col = brewer.pal(4,"RdYlGn"))
> 

If you look at the links from ?spplot, then ?levelplot explains what 
is happening:


at: A numeric vector giving breakpoints along the range of ‘z’.
    Contours (if any) will be drawn at these heights, and the
    regions in between would be colored using ‘col.regions’.  In
    the latter case, values outside the range of ‘at’ will not be
    drawn at all.  This serves as a way to limit the range of the
    data shown, similar to what a ‘zlim’ argument might have been
    used for.  However, this also means that when supplying ‘at’
    explicitly, one has to be careful to include values outside
    the range of ‘z’ to ensure that all the data are shown.

When using base graphics, the classInt package takes care to let the 
user specify how to define the breakpoints (via arguments to 
findIntervals), but no provision is made for spplot or lattice 
graphics as such. Consequently, at present you need to add a very 
small value to the top breakpoint, and subtract from the bottom 
for symmetry:

brks <- classIntervals(spdf$weight,4)$brks
eps <- .Machine$double.eps
brks[1] <- brks[1] - eps
brks[length(brks)] <- brks[length(brks)] + eps
spplot(spdf, "weight", at=brks)

for some suitable value of eps. Note that the default class intervals 
are by quantile.

Please consider the R-sig-geo list for questions of this kind - thank 
you for including a simple working example.

Hope this clarifies,

Roger