[R-sig-Geo] fix color scale

[Edzer Pebesma]

Paul, this nicely illustrates the power of ggplot2.

In the resulting plot, however, it seems to me that the

+ opts(aspect.ratio = 1)

does not result in the desired effect that 1 m in the x direction equals
1 m in the y direction. Standard plot (asp = 1), and lattice plots (asp
= "iso") have this; what does ggplot2 need?

On 10/31/2010 11:31 AM, Paul Hiemstra wrote:
> Hi Peter,
> 
> When creating such a large amount of illustrations with the same
> colorscale, I automatically think of lattice graphics. Under the hood
> spplot also uses lattice graphics. Take a look at the levelplot()
> function from lattice which produces the grid plots for spplot (if I'm
> correct). Alternatively, I've been using ggplot now for quite a while to
> make plots of a lot of grids. A small example says more than a thousand
> words:
> 
> library(ggplot2)
> library(sp)
> 
> data(meuse.grid)
> summary(meuse.grid)
> 
> # Note that I do not transform meuse.grid to SpatialPixelsDataFrame
> # Let's make a simple grid plot
> dum = meuse.grid[c("x","y","dist")]
> ggplot(aes(x = x, y = y, fill = dist), data = dum) + geom_tile()
> 
> # Let's make a few more attributes to the grid
> # could be measurements on other dates for example
> new_atts = do.call("cbind", lapply(1:100, function(num) dum$dist +
> runif(dum$dist)))
> summary(new_atts)
> dum = data.frame(cbind(dum, new_atts))
> 
> # Important step now is to
> # restructure the data
> dum_ggplot = melt(dum, id.vars = c("x","y"))
> 
> # Now make a plot using dum_ggplot
> # of 'x' and 'y' using value as a 'fill'
> # with a plot per 'variable', can take a minute to plot
> ggplot(aes(x = x, y = y, fill = value), data = dum_ggplot) + geom_tile()
> + facet_wrap(~variable) +
>       scale_x_continuous('', labels = NA, breaks = NA) +
>       scale_y_continuous('', labels = NA, breaks = NA) +
> opts(aspect.ratio = 1)
> # These last two lines get rid of the labels on the axes and set aspect
> ratio to 1
> 
> Now you have a plot with 101 maps with the same colorscale, with ggplot
> doing all the hard work. It takes some time to get the hang of ggplot,
> but I think it is worth the investment, also for spatial plots.
> 
> cheers and hope this helps,
> Paul
> 
> On 10/28/2010 09:12 PM, Peter Larson wrote:
>> Hello!
>>
>> I have a problem.
>>
>> I am using IDW to interpolate a daily series of geospatial
>> observations. Thus, I want to produce a large number of sequential
>> maps.
>>
>> I want them to all represent the same color scale. Is there any way to
>> fix the color scale so that it is the same for all the plots?
>>
>> Thanks,
>>
>> Pete
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>    
> 
> 

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de