Takes an ‘mask’ type polygon object - basically a rectangle with a polygon hole cut through it - and draws this over an image. This has the effect of only showing the image inside the hole. This is useful for plotting surfaces defined over a study area, but masking the values outside of the area.
A masking polygon as described above.
Colour of the mask. Defaults to white, but for example, sea could be shown as blue.
Returns no value, but draws a mask on the current graphics device as a side effect
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# Data for New Haven to use in example data(newhaven) # Do the KDE breach.dens = kde.points(breach,lims=tracts) # Plot the result level.plot(breach.dens) # Block out the part outside the study area masker = poly.outer(breach.dens,tracts,extend=100); add.masking(masker) # Plot census tract boundaries plot(tracts,add=TRUE)
Loading required package: maptools Loading required package: sp Checking rgeos availability: TRUE Loading required package: RColorBrewer Loading required package: MASS Loading required package: rgeos rgeos version: 0.3-23, (SVN revision 546) GEOS runtime version: 3.4.2-CAPI-1.8.2 r3921 Linking to sp version: 1.2-3 Polygon checking: TRUE NOTE: rgdal::checkCRSArgs: no proj_defs.dat in PROJ.4 shared files
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