hi all,<br><br>i'm interested in estimating the centre of population of a city and how it might have changed in 10 years. i have a vector polygon layer for each year, which is the ward population. each layer has 198 polygons(wards) with population attributes for each polygon(ward). The distribution of population within a ward is not known, hence assumed uniform for now.<br clear="all">
<br>is there a module in GRASS for calculating this. i know we can calculate geographic centroids, but was'nt sure if there was one for this kind of thing.<br><br>Otherwise i could do it manually by extracting the geographic centroid of each polygon, then the coordinates of the population centre would be:<br>
<br>xhat = sum(Pi Xi) /(sum(Pi)<br>yhat = sum(Pi Yi) / sum(Pi)<br><br>where Xi, Yi are each polygon i's geographic centroids; and Pi are each polygon's population<br>coordinates are in UTM.<br><br>what do you think?<br>
<br>Thanks,<br>Vishal<br>-- <br>Vishal K. Mehta, PhD<br>Scientist<br>Stockholm Environment Institute - US<br>133 D St Suite F<br>Davis CA 95616<br><a href="http://www.sei-us.org">www.sei-us.org</a><br>