[GRASS-stats] Spatial categories for risk data.

[Hamish]

> I currently have a map that looks something like this: 
...
> Each letter represents a
> person, and the entire map represents a state. Each
> person’s “risk score” is a continuous numeric value, but I have
> categorized it into low,
> moderate, and high for visual simplicity. What I’m
> hoping to do is draw
> lines that will divide out the categories. The lines do not
> have to necessarily
> be straight, but I would like them to be simple enough. I
> figure that I would
> have to account for any overlapping or outlying persons.
> This is my initial
> idea of how the map would turn out: 
...
> I have downloaded and
> installed GRASS and R, but I am not sure what type of
> spatial method or
> analysis to use. Could someone please offer me advice on
> how to get started with this project? Thanks so much! 


keeping within grass, a possible solution is to use v.surf.rst
to make a spline fit to the data (adjust tension= and smooth= 
parameters and region resolution to suit), then if more
smoothing is needed use the r.neighbors module with a suitable
search distance.

finally use r.contour to set up your isolines at whatever
thresholds you use for risk category.

if you like you could use r.colors on the "elevation" map to
show it as solid red/yellow/green bands; see also the
r.colors.stddev module for setting the color table.


there's a v.kernel module, but I don't know much about that.


Hamish