[R-sig-Geo] spplot question

[Roger Bivand]

On Fri, 11 Sep 2009, Eric Morway wrote:

>
> Edzer,
>
> I apologize for the confusion.  Is there an option in spplot that fills in 
> blank/white cells (I'm assuming they are blank because they have a value less 
> than the minimum cut) with the minimum color on the legend bar (in this case 
> green)?  About a quarter of the way in from the left edge of the image you'll 
> notice a "hole" in the plot due to these cells having values less than 10.  I 
> would like to fill these cells in without altering the legend, if possible.

No, please see the help page for levelplot() in lattice, the at= argument 
is describes as follows:

       at: 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.

So you'll need to adjust your at= to accommodate all of the data.

Roger


>
> Thanks, Eric
>
> Edzer Pebesma wrote:
>> Eric, I've been reading your email over and over, but cannot understand
>> what you want. I also could not find a question, despite your subject.
>> --
>> Edzer
>> 
>> Eric Morway wrote:
>> 
>>> Hello,
>>> 
>>> I've been working on an image created with spplot and with help have
>>> gotten it very close to the final product.  One final modification I
>>> would like to make involves filling in grid cells with values less
>>> than the minimum value on the legend with the color corresponding to
>>> the bottom of the legend.  In the attached figure, the minimum legend
>>> value is 10, but there a few spots with values as low as 0.01. These
>>> cells are currently blank/white.  I would like to avoid including this
>>> value on my legend due to the color spread on the plot becoming
>>> homologous, that is, I would like the color spread to be maximized
>>> between 10-1000.  Were I to go from 0.01-1000, the range I'm most
>>> interested in (10-1000) would be confined to a more narrow range of
>>> the legend.  I have played around with trying to specify a different
>>> number of cuts for the legend vs plot area, but this causes a
>>> disconnect between the legend and the colors displayed for the
>>> different grid cells.  The spplot line looks like this (image attached):
>>> 
>>> pts<-list("sp.points",K.dat,pch=3,col="black",labels=as.character(K.dat$Kh))
>>> 
>>> cuts<-c(10,20,30,40,50,60,70,80,90,100,200,300,400,500,600,700,800,900,1000)
>>> 
>>> spplot(lzm.krige.dir["var1.pred"],at=cuts,colorkey=list(at=log10(cuts),labels=as.character(cuts)),scales=list(draw=TRUE),
>>>  xlab="Easting",ylab="Northing",key.space="right",cex=1.1,col.regions=terrain.colors(22),main="Hydraulic
>>> Conductivity of Layer 2",sp.layout=list(pts))
>>> 
>>> Respectfully,
>>> Eric Morway
>>> 
>>> ------------------------------------------------------------------------
>>> 
>>> ------------------------------------------------------------------------
>>> 
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>> 
>> 
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no