Is there anyway to calculate population weighted centroids of a spatial polygon in R? Any idea will be appreciated. Thanks Zia -- --------------------- Zia Ahmed, PhD Research Associate Department of Crop and Soil Sciences 1002 Bradfield Hall, Cornell University Ithaca, NY 14853-4203 t. 607.255.9387 f. 607.255.3207 email zua3 at cornell.edu