[R-sig-Geo] How to draw grid contours within a map

[Thiago Veloso]

  Dear R-Siggers,

  In order to illustrate the spatial domain of the General Circulation Model (GCM) output data I am using, I need to display some grids within a map. They need to be 2.5°x2.5° lat-lon over specific coordinates. Actually, I am trying to partially reproduce Figure 1 inside Challinor et al., 2005 (image attached).

  To load and display the shapefile I use the following code:

library(maptools)
southern=readShapePoly("D:/Maps/papers-in-progress/regiao_sul.shp")
plot(southern)

  Following, I create the "empty" grids to draw:

library(raster)
rprecip<-raster(xmn=-60,xmx=-50,ymn=-35,ymx=-25)
res(rprecip)<-2.5

  But I am stuck on the task of displaying those grids on the map.

  Could anybody please point any directions?

  Best,

  Thiago.


      
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