[R-sig-Geo] Optimize image plot of a grid with legend - colors - and extras ?

[Roger Bivand]

On Mon, 4 Jun 2007 Jan.Verbesselt at csiro.au wrote:

> Hi Roger,
> 
> I made a reproducible example: When you change the colors of the spatial
> image the colors of the axes also change. How could this be solved?

Because the col= argument is passed using the "..." mechanism, it is seen 
twice in the image() method (once to draw the axes, next to draw the 
image) unless add=TRUE. So:

plot(as(input, "Spatial"), axes=TRUE)
image(input, col=kleur, main = paste("meuse river data set;",
"colour indicates distance to river"), add=TRUE)

works. col.axis in par() only sets the colour of the axis annotation, and 
is not used here.

> 
> (How can a legend and scale be added to this plot?)
> 

In principle, the axes give the cardinal directions and the scale.  
Although this is cartographic heresy, I have not seen anyone with a ruler
using a scale on a computer display to read off distances, so that
inserting a scale is probably overkill, the same with the north arrow. It
can be done for presentation purposes, or if a reader demands it, but it
is redundant is axes=TRUE. If axes=FALSE, then hand construction with
lines() and text() (arrows() for N arrow) isn't hard.

The legend can be added as you suggest, or using a similar function in 
geoR. Both involve placing manually - which could be improved by using the 
placing names from legend(), but still give no guarantee that content will 
not be overpainted. Perhaps the function from geoR could be migrated to 
sp, since geoR now depends on sp.

> All other tips and tricks are mostly welcome,
> 
> Thanks a lot,
> Jan
> 
> Ps. Great that this sp() package make spatial analysis and visualization
> possible in R! - Does maptools package offer better or alternative
> mapping functions? 

The sp package provides classes and methods for Spatial*, maptools 
provides tools for simple import/export and interfaces to other R 
packages, rgdal more advanced import/export. None are designed to provide 
presentation cartographic output - they provide analytic graphics, and the 
functions to export the data if you need something more fancy. 

I find that users put far too much time into presentation, losing touch
with what the data are telling them. My understanding of data
visualisation is that communication depends on getting the important
things across, which are the data, and an unobtrusive support for position
(the real "map" is its representation inside the computer, not the
hardcopy output).

For example, informative setting of the class intervals is important - 
using the defaults in image() can be very deceptive.

Hope this helps,

Roger

> 
> /***script***
> 
> library(fields)
> library(sp)
> 
> data(meuse.grid)
> coordinates(meuse.grid) = ~x+y
> gridded(meuse.grid) = TRUE
> data(meuse)
> coordinates(meuse) = ~x+y
> data(meuse.riv)
> plot(meuse.riv)
> meuse.sl = SpatialLines(list(Lines(list(Line(meuse.riv)))))
> 
> ## image plot with points and lines
> nr <- 200
> ramp <- colorRamp(c("blue", "green"))
> kleur <- rgb( ramp(seq(0, 1, length = nr)), max = 255)
> par( mar=c(5,5,5,8))
> input <- meuse.grid["dist"]
> image(input, col=kleur, axes=T,main = "meuse river data set; colour
> indicates distance to river", col.axis=1)
> points(meuse, pch = 3)
> plot(meuse.sl, add=T)
> image.plot( zlim=c(min(input$dist),max(input$dist)),
> nlevel=nr,legend.only=TRUE, horizontal=F, col=kleur)
> 
> 
> 
> 
> -----Original Message-----
> From: Roger Bivand [mailto:Roger.Bivand at nhh.no] 
> Sent: Friday, 1 June 2007 7:01 PM
> To: Verbesselt, Jan (Ensis, Clayton)
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: Optimize image plot of a grid with legend - colors - and
> extras ?
> 
> On Fri, 1 Jun 2007 Jan.Verbesselt at csiro.au wrote:
> 
> > Thanks Roger,
> > 
> > It's all working now ; I plotted a shape file on top of a spatial grid
> > image via the following script. Only, when you change the colors of
> the
> > image() the axis colors also change. I couldn't solve this and tried
> > several options (par, axis(), etc), but nothing worked.
> 
> In order to find this out, please provide an example with the meuse.grid
> 
> dataset shipped with sp, and for the shape, the meuse.riv river contour.
> 
> It may be that the col= argument is being passed through by accident to 
> plot.Spatial(), but without a reproducible example, it is difficult to 
> say.
> 
> Roger
> 
> > 
> > I also used image.plot() of the fields library to add a legend to the
> > image.
> > 
> > Does somebody has some advise how to optimize these type of spatial
> > image -grid plots with a legend, colors, and other extra's? 
> > 
> > All examples are welcome,
> > Cheers and thanks,
> > Jan
> > 
> > 
> > # combining the  usual image function and adding a legend
> > # first change margin for some more room
> > nr <- 100
> > ramp <- colorRamp(c("blue", "green"))
> > kleur <- rgb( ramp(seq(0, 1, length = nr)), max = 255)
> > par( mar=c(5,5,5,8), col.axis =1)
> > image(GRID, col=kleur, axes=T)
> > plot(shape,add =TRUE , border = "red", axes=F, las=1)
> > image.plot( zlim=c(min(data["ndvi"]),max(data["ndvi"])),
> > nlevel=nr,legend.only=TRUE, horizontal=F, col=kleur)
> > box()
> > 
> > 
> > 
> 
> 

-- 
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