Date:         Thu, 3 Mar 2005 12:08:24 -0500
Reply-To:     "Michael S. Zdeb" <msz03@HEALTH.STATE.NY.US>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "Michael S. Zdeb" <msz03@HEALTH.STATE.NY.US>
Subject:      Re: Center of Population
Content-type: text/plain; charset=US-ASCII

Hi...as Jack Hamilton mentioned in an earlier posting, PROC SUMNMARY  makes
it pretty easy...based on...

http://www.uiowa.edu/~gishlth/UIORNL/2_SEER_reportl_ornl_0304.pdf

(page 8 - Algorithm for Population Centroids Derivation)

It's just a population weighted average of the centroids of the smaller
units.  So, here are Albany county (NY) zip codes....x and y centroids in
radians.  I think that this will work OK.....

data albany;
input zip x y pop;
datalines;
   12009    1.29216    0.74521     7628
   12023    1.29451    0.74360     2121
   12041    1.29126    0.74275       14
   12046    1.29002    0.74162      934
   12047    1.28673    0.74669    18167
   12054    1.28922    0.74360    16421
   12059    1.29257    0.74375     1843
   12067    1.29017    0.74277     1854
   12077    1.28776    0.74344     5719
   12084    1.28980    0.74525     4214
   12110    1.28762    0.74617    20463
   12120    1.29398    0.74102      539
   12143    1.28894    0.74154     5348
   12147    1.29413    0.74198      528
   12158    1.28839    0.74250     5779
   12159    1.28947    0.74427     7646
   12183    1.28614    0.74608     2278
   12186    1.29104    0.74402     6461
   12189    1.28657    0.74585    16783
   12193    1.29229    0.74201     2117
   12202    1.28738    0.74408    10021
   12203    1.28881    0.74490    32866
   12204    1.28682    0.74500     6792
   12205    1.28848    0.74552    26337
   12206    1.28766    0.74478    16291
   12207    1.28713    0.74442     2187
   12208    1.28814    0.74438    21307
   12209    1.28781    0.74416     9772
   12210    1.28726    0.74451     9492
   12211    1.28735    0.74534    10684
   12303    1.29022    0.74610    27942
   12469    1.29568    0.74086      783
;
run;

proc summary data=albany;
var x y;
weight pop;
output out=centroids (keep=cx cy) mean=cx cy;
run;

title 'Albany County Population Centroid - Based on ZIP Aggregation';
proc print data=centroids;
run;


Mike Zdeb
U@Albany School of Public Health
1 University Drive
Rensselaer, NY   12144-3456
(P)518-402-6479
(F)630-604-1475