[postgis-users] quantiles, quartiles, or jenks natural

Robert Burgholzer rburghol at chesapeakebay.net
Thu Mar 2 06:40:32 PST 2006

I'm coming into this late, but I am a user of PL/R and PostGIS, and
would appreciate any progress on developing some classification routines
to be posted to this lists, or I would be interested in being notified



-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Amit
Sent: Wednesday, March 01, 2006 1:20 PM
To: postgis-users at postgis.refractions.net
Subject: Re: [postgis-users] quantiles, quartiles, or jenks natural

Sorry, I have been catching up on the past few months emails. I just
want to add that I read that quantiles and minimum boundary error are
better than jenks. Also minimum boundary error takes into account the
underlying topology.

The two being better are mentioned in 

Brewer, Cynthia A. & Pickle, Linda (2002) Evaluation of Methods for
Classifying Epidemiological Data on Choropleth Maps in Series.
Annals of the Association of American Geographers 92 (4), 662-681

And the minimum boundary algorithm is supposedly mentioned in 

Cromley, E. K. , and R. G. Cromley. 1996. An analysis of alternative
classification  schemes  for  medical  atlas mapping. European Journal
of Cancer 32A (9): 1551 -- 59. 

Cromley, R. G. , and R. D. Mrozinski. 1999. The classification of
ordinal data for choropleth mapping. The Cartographic Journal 36 (2):
101 -- 9.


Date: Tue, 14 Feb 2006 12:38:39 -0800
From: Paul Ramsey <pramsey at refractions.net>

I did some in PHP, but the algorithms are relatively braindead, the  
quantile stuff in particular.  Jenks I did some research on but never  
really found a definitive description of the process.  Some of the  
descriptions ended up sounding like a k-means clustering idea, which  
is not cheap!


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