GeoNames Forum

I'm attempting to build a lookup service based off the 'allcountries' dump such that a user can input a country code and postal code and have the centroid latitude & longitude returned. This is simple enough for most postal codes, but I run into a problem with postal codes that have multiple entries. For example, the postal code '4126' in AR has several entries; is there an acceptable way for me to compute the centroid of the entire postal code from this data? It seems that simply averaging the coordinates would not be accurate.

AR 4126 MIRAFLORES (TALA, DPTO. CANDELARIA) SALTA A -26.0833 -65.263 3
AR 4126 EL BRETE SALTA A -26.0667 -65.3667 4
AR 4126 LA MARAVILLA SALTA A -26.0833 -65.263 3
AR 4126 RUIZ DE LOS LLANOS SALTA A -26.1167 -65.2833 4
AR 4126 EL CUIBAL SALTA A -26.0833 -65.263 3
AR 4126 CEIBAL SALTA A -26.1 -65.0167 4
AR 4126 EL SUNCHAL SALTA A -26.0833 -65.263 3
AR 4126 BRETE SALTA A -26.0667 -65.3667 4
AR 4126 OVEJERO SALTA A -26.0833 -65.263 3
AR 4126 CANDELARIA SALTA A -26.1 -65.1 4
AR 4126 SAN PEDRO DE ARANDA SALTA A -26.0833 -65.263 3
AR 4126 EL JARDIN SALTA A -26.0833 -65.3833 4
AR 4126 SALAZAR SALTA A -26.0833 -65.263 3
AR 4126 LOS MOGOTES SALTA A -26.0333 -65.2 4
AR 4126 ALEM SALTA A -26.0833 -65.263 3
AR 4126 TALA SALTA A -26.1167 -65.2833 4
AR 4126 BARADERO SALTA A -26.0833 -65.263 3
AR 4126 LA ASUNCION SALTA A -26.0833 -65.263 3