R GIS: Polygon Intersection with gIntersection{rgeos}

September 16, 2013
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A short tutorial on doing intersections in R GIS. gIntersection{rgeos} will pick the polygons of the first submitted polygon contained within the second poylgon – this is done without cutting the polygon’s edges which cross the clip source polygon. For the function that I use to download the example data, url_shp_to_spdf() please see HERE.

library(rgeos)
library(dismo)

URLs <- c("http://gis.tirol.gv.at/ogd/umwelt/wasser/wis_gew_pl.zip", # all water bodies in Tyrol
"http://gis.tirol.gv.at/ogd/umwelt/wasser/wis_tseepeicher_pl.zip") # only artificial..

y <- lapply(URLs, url_shp_to_spdf)
z <- unlist(unlist(y))
a <- getData('GADM', country = "AT", level = 2)

b <- a[a$NAME_2=="Innsbruck Land", ] # political district's boundaries
c <- spTransform(b, z[[1]]@proj4string)
z1_c <- gIntersection(z[[1]], c, byid = TRUE)
z2_c <- gIntersection(z[[2]], c, byid = TRUE)

plot(c)
plot(z1_c, lwd = 5, border = "red", add = T)
plot(z2_c, lwd = 5, border = "green", add = T)
plot(z[[1]], border = "blue", add = T) # I plot this on top, so it will be easier to identify
plot(z[[2]], border = "brown", add = T)

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