[R-sig-Geo] [FORGED] kernel density: units of bandwidth

Rolf Turner r.turner at auckland.ac.nz
Mon Feb 22 21:08:44 CET 2016

On 20/02/16 13:48, Tadaishi Yatabe-Rodriguez wrote:
> Hello community,
> I did a lovely kernel density from a point pattern, but now I'm wondering
> what was the actual bandwidth I used. The value I used was 0.2770598, but
> what does this mean? I suppose it's an area, but what is the unit? Is there
> a way to transform this into a meaningful area unit?

As the help for density.ppp tells you, sigma is the standard deviation 
of the isotropic Gaussian "smoothing kernel" (i.e. density function with
mean c(0,0) and standard deviation of both "X" and "Y" equal to sigma, 
and cov(X,Y) = 0).  Consequently the units of sigma are the units in 
which X and Y are measured.

Thus if, for example, your point coordinates are in metres, then the 
units of sigma are metres.  (So sigma is measured not in area but in 
length or distance.)



Rolf Turner

Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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