Re: [S] Pie Diagrams

Jim Hodges (hodges@ccbr.umn.edu)
Fri, 13 Nov 1998 08:30:22 -0600 (CST)


Thanks to Robert Garrett for sending the example, but for my money it'd
still be better to make a bunch of little bar charts than a bunch of
little pie charts. If the bar charts were all on the same scale, you
could still convey both kinds of information and it would, per Cleveland,
be perceptually superior.

Jim Hodges

&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
&& &&
&& Jim Hodges Phone: (612) 626-9626 &&
&& Division of Biostatistics Fax: (612) 626-8892 &&
&& School of Public Health e-mail: hodges@gopher. &&
&& University of Minnesota ccbr.umn.edu &&
&& 2221 University Ave SE, Suite 200 &&
&& Minneapolis, Minnesota 55414 &&
&& &&
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&

On Fri, 13 Nov 1998, Garrett, Robert wrote:

> I agree that Pie Diagrams have their problems, but I would like to give one
> example where they did help visualization of a complex spatial data set.
>
> Heavy minerals were separated from glacial tills in the Canadian Prairies
> and semi-quantitatively analysed. As a result the data set consisted of a
> spatial location, the total weight of heavy minerals separated, mg/kg, and
> the weights, mg, of the individual types of heavy minerals for some 816
> sites. An initial investigation showed that six of the heavy mineral types
> provided useful information for identifying the regions which were the
> sources of the glacial tills, but that absolute weight of heavy minerals was
> important. The solution to vizualizing this data set was to plot pies at
> their spatial locations on a map where the diameter of the pie was
> proportional to the sum of the six heavy mineral weights, and the pie was
> divided and coloured in proprtion to the contributions of the six heavy
> minerals. This provided a vizualition where the seven important variates
> were displayed in a form that allowed recognition of individual glacial
> tills with characteristic heavy mineral assemblages in the Canadian Prairie
> region, and provided geologists with information they could use to ascertain
> the sources areas of the tills.
>
> I realize that this is a very specific case, but it demonstarates two
> things. Firstly, a very wide range of scientists/economist/others are
> interested in data vizualiztion (few geoscientists are heard from on S-News,
> but I learn an enormous amount from the participants to S-News); and
> secondly, despite drawbacks there are cases where a procedure, despite its
> drawbacks, can provide a useful visualization. The case above demonstrates
> this point, where seven variates were of simultaneous relevance and interest
> to a problem.
>
> Robert G. (Bob) Garrett
> Applied Geochemistry and Geophysics
> Subdivision
> Geological Survey of Canada
> 601 Booth St., Ottawa, Ontario K1A 0E8
> Internet: garrett@gsc.NRCan.gc.ca
> Tel.: 613+995-4517 FAX: 613+996-3726
> ----------------------------------------------------------------------
>
>
>
> -----------------------------------------------------------------------
> This message was distributed by s-news@wubios.wustl.edu. To unsubscribe
> send e-mail to s-news-request@wubios.wustl.edu with the BODY of the
> message: unsubscribe s-news
>

-----------------------------------------------------------------------
This message was distributed by s-news@wubios.wustl.edu. To unsubscribe
send e-mail to s-news-request@wubios.wustl.edu with the BODY of the
message: unsubscribe s-news