Both the West and East coast of the US have the wealthiest ZIP codes (area codes), according to data compiled for Advertising Age’s American...

Both the West and East coast of the US have the wealthiest ZIP codes (area codes), according to data compiled for Advertising Age’s American Demographics by ESRI, a supplier of geographic information-systems software and data.

Metropolitan New York is home to nearly half (24) of the richest 50 ZIPs. Add in Boston (five), Philadelphia’s Main Line (two) and suburban Washington (one), and the Northeast corridor accounts for 32 out of 50 of the most-prized ZIP codes.

The 50 ZIPs are home to 201,799 households and 565,125 residents. This elite group, which makes up just 0.2 per cent of the US population, last year had an average household income of $294,000, four times the national average ($67,572), and average net worth of $1.2 million, about three times the national figure ($468,970), according to the research.

The top 10 ZIPs, from No. 1 Atherton in California, to Old Westbury in New York, are all on the coasts of the US.

ESRI ranked ZIP codes based on a formula including such demographic variables as average household income and average net worth. Surging real estate prices on the coasts have boosted the net worth of households in those regions. But coastal communities also pay better; the coasts are home to nine of the 10 ZIPs with highest household income.

The research found six affluent ZIPs in San Francisco and Silicon Valley, which together form the money centre of the West. Los Angeles has just four. Its most celebrated address, Beverly Hills 90210, came in a distant No. 35 nationally, reflecting in part that the ZIP is home to both glitzy houses and not-so-ritzy apartments. Beverly Hills ranked second-lowest in median income.

The Northeast of the US accounts for nearly two-thirds of the wealthiest ZIPs (32) and more than half of the affluent ZIPs’ population (about 320,000). The greater New York area is home to 24 top ZIPs and 256,000 residents. Two of the nation’s hubs of old money, Philadelphia and Boston, account for most of the region’s remaining wealthy ZIPs.

The research found population growth to be low in the wealthiest ZIPs. ESRI projects slow growth for the richest ZIPs in the Northeast and Midwest; it expects only two of the 35 will see growth greater than one per cent a year through 2009. In the West, four of the 14 rich ZIPs should see greater than one per cent growth. Atlanta’s rich ZIP should grow 1.5 per cent a year.

The West Coast of the US is the new home for older money, with the median age of the rich list’s 14 West Coast ZIPs being 46, four to five years above that of affluent ZIPs in other regions. The median age in Los Altos, a pillar of Silicon Valley, is above that of desert oasis Paradise Valley. Median ages for the rich ZIPs in Northern California and Los Angeles are around the mid-40s.