[R-sig-Geo] Map layer

[Paul Hiemstra]

Hi Fernando,

If you use the sp classes for spatial data you can use the spplot 
function to make very nice plots. See 
http://cran.r-project.org/doc/Rnews/Rnews_2005-2.pdf for more 
information on sp. See 
http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:import_export 
for information on how to import your data into sp-classes.

In regard to your problem with the points outside the map. If your data 
is stored in sp objects you can use the overlay() function from the 
sp-package to determine which points are outside the polygon, see 
?overlay for more details. Those points can be deleted from the 
sp-object and they will not appear in the plot.

hth,

Paul

Fernando Miguez wrote:
> Hi all,
>
> I would like to be able to do the following
>
> map('state','illinois')
> points(x,y)
>
> Up to this point everything is fine. However, some of the points fall 
> outside the Illinois map boundaries. What I would like to do is to add 
> a layer where the inside of the Illinois polygon is transparent (so 
> that the points can be seen) but the points outside the boundary are 
> covered so they are not seen. I thought that using some variation of 
> map with its arguments would work, but I haven't been able to figure 
> it out. I see that it is quite possible that I'm using the wrong tools 
> all together ... let me know.
>
> Any help is appreciated. Thanks.
>
> Fernando
>


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: 	+31302535773
Fax:	+31302531145
http://intamap.geo.uu.nl/~paul