[R-sig-Geo] raster package display

[Barry Rowlingson]

On Wed, Jun 29, 2011 at 4:50 PM, Colin Robertson <colinr23 at gmail.com> wrote:
> Dear List,
>
> I am creating a raster as the output of a function, and for testing
> purposes the output of this function should be a raster with all 1's.
>
> When I check with summary, this is the case:
>
> class(out[[2]])
> [1] "RasterLayer"
> attr(,"package")
> [1] "raster"
>
> summary(out[[2]])
> Cells:  1600
> NAs  :  304
>
> Min.      1
> 1st Qu.   1
> Median    1
> Mean      1
> 3rd Qu.   1
> Max.      1
> NA's    304
>
> Yet when I plot using plot(out[[2]]), I get a display of values
> ranging from 0.6 - 1.4.
>
> All summaries on the raster indicates all cells have value of 1, but
> the display shows differently.
>
> Any ideas on what is happening here much appreciated,

 I suspect - and a quick look at the code will confirm it - that it
just decides to expand the key a bit because your values are all 1.

 The image.plot function in the fields package does the same thing for
a matrix of all the same values.

 In a way it's not lying, because its showing you all the cells with
value 1 are the same colour. It's just not showing you that there are
no cells with any other colour. I guess a scale with 1 at the top,
middle, and bottom would look odd.

 If you add a zlim parameter you can get something that may be a bit
more meaningful:

 m=raster(matrix(1,10,10))
 plot(m)
 plot(m,zlim=c(0.99,1.01))

 - the colour ramp then shows you there's nothing at 1.010, since
there's nothing green on the plot...

Barry