[R-sig-Geo] classInterval(style="fisher") vs. ArcView GIS natural breaks

[Roger Bivand]

On Fri, 16 Mar 2007, Hervé Polesi wrote:

> Hi!
> 
> Working on a litle datebase (903 lines) I notice a difference between 
> the result of classInterval(style="fisher") and the natural breaks 
> proposed by ArcView GIS (3.2).
> I read that ArcView works on a sample of data. Is it right ? May it 
> cause a significative difference ?

The classInt package is open source, but ArcView/ArcGIS isn't (unless you 
consider the new python scripts, but I don't think these include class 
intervals). Is it possible to check in the ESRI documentation? I recall 
being told that the symbology is built on the fly and probably stored in 
the project, and that a sample is used instead of the total. If anyone 
has some students who'd like to deconstruct the ESRI approach by testing 
on known distributions, that might be fun. We have the Fisher code (as 
implemented), so seeing why things might differ ought to be possible.

Of course, there are very many different classifications anyway, even for 
moderate n and k.

Best wishes,

Roger

> 
> Greetings from Strasbourg, France.
> 
> Hervé Polesi
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no