R - Rasterize a SpatialPolygonsDataFrame - variables/attributes dropped

Question

Whenever I rasterize my SpatialPolygonsDataFrame, I lose the attribute / data information part. The command "rasterize" is from the package "raster" in R.

I have the following RasterLayer (named "raster1")

class       : RasterLayer 
dimensions  : 6000, 4800, 28800000  (nrow, ncol, ncell)
resolution  : 0.00025, 0.00015  (x, y)
extent      : 8.699875, 9.899875, 46.69993, 47.59993  (xmin, xmax, ymin, ymax)
coord. ref. : +init=epsg:3857 +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs

My SpatialPolygonsDataFrame (named "bw1") has the following properties

class       : SpatialPolygonsDataFrame 
features    : 7663 
extent      : 980075.6, 1076577, 5908811, 6023151  (xmin, xmax, ymin, ymax)
coord. ref. : +init=epsg:3857 +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs 
variables   : 2
names       :    A,  B 
min values  : 3231, 11 
max values  : 3955, 19

When I use a the command

bw1_raster<-rasterize(bw1,raster1,fun='last',field=c("A","B")

I get the new object "bw1_raster":

class       : RasterLayer 
dimensions  : 6000, 4800, 28800000  (nrow, ncol, ncell)
resolution  : 0.00025, 0.00015  (x, y)
extent      : 8.699875, 9.899875, 46.69993, 47.59993  (xmin, xmax, ymin, ymax)
coord. ref. : +init=epsg:3857 +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 
+lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs 
data source : in memory
names       : layer     
values      : NA, NA  (min, max)

How do I get a raster object with attributes / layers "A" and "B"?

Robert Hijmans · Accepted Answer · 2016-07-10 16:36:16Z

1

The problem is that the coordinate reference system of the SpatialPolygons do not match that of the RasterLayer. It looks like they match, but that is probably because you changed the crs of the RasterLayer to an incorrect value. The RasterLayer almost certainly has a longlat crs, not merc.

You need to assign it the correct crs (or at least do not change it to a wrong one!).

Depending on what you want to achieve, you could use spTransform to transfrom the SpatialPolygons to the crs of the RasterLayer and try again.

Alternatively, you could do something along these lines

library(raster)
r <- raster(bw1, res=10000)
r <- rasterize(bw1, r)

answered Jul 10, 2016 at 16:36

Robert Hijmans

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