[GRASSLIST:1581] Re: interpolate nominal values

[Rich Shepard]

On Thu, 8 Mar 2001, Lyle E. Browning wrote:

> Archaeologists use this sort of info all the time, although it could be argued
> that we don't live in the real world either ;>)

Lyle,

  I won't touch that one, thank you!

> Isn't that exactly the kind of info that those fast-food mega-corps used in the
> first place to locate their gut grenade establishments? Population dynamics,
> transportation nodes, economic bases, etc.

  This is a flour from a different mill. Performing a nearest-neighbor
analysis by fitting Veronoi polygons around each fast-food outlet will show
all the points that are closer to one burger than another. However, while
this is interpolation (finding the midline between all adjacent pairs of
points) you could not proceed to build an elevation model from it and have
the resulting surface mean anything.

  With the soils data that initiated this thread, the point represents an
area. Veronoi polygons don't mean anything here, and producing a 3D surface
map is equally meaningless. And that's where the discussion went: how do you
interpolate a surface from the point data?

  Perhaps you build 3D continuous surfaces from pottery shards or flour mill
locations, and it means something within the field of archaeology. But, as
a quantitative ecologist, I'd map the soils data and all I could say is
that's the soil type at this point. Period.

  One of my undergraduate chemistry profs (from whom I took inorganic and
physical chemistry) told me he couldn't understand how anyone could be a
field biologist. "After all," he said, "everything is a variable. Nothing is
a constant. How can you make sense of it?" "Statistics," I replied. "And
mumbling with big words when that doesn't help." :-)

  Actually, I think this thread is quite appropriate for the GRASSlist.
Knowing the mechanics of running the software does not qualify the operator
as a spatial analyst. As we are all well aware, teaching someone how to
manipulate a word processor does not make him a good writer. I like this
discussion.

Rich

Dr. Richard B. Shepard, President

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