Most expensive ZIP codes

Methodology
We based our rankings on the median home sale prices in 2005 for each ZIP, nearly all of them collected by New York City-based real estate data firm OnBoard. For Manhattan, where more than 80% of the homes are co-operative apartments, we turned to real estate consulting and appraisal firm Miller Samuel.

OnBoard collects residential, arms-length real property transactions for counties covering approximately 80% of all U.S. households, with a focus on metropolitan and suburban areas. It excludes sales under $25,000, vacant land and co-operative sales. We also tossed out ZIP codes that had fewer than 20 sales last year. In states where property transactions aren't publicly disclosed, some percentage of sale values may have been estimated using industry-standard ratios to the mortgage amount. The place name for each ZIP is the U.S. Postal Service's "preferred" city name for postal delivery.

We also included some other ZIP code information supplied by OnBoard. The company estimates median household income using data from the U.S. Census Bureau and the Bureau of Economic Analysis. ZIP code population, population change and median age estimates are calculated using data from the Census Bureau, analysis of building permits and the latest county population estimates; household size is projected from state and Census data.

OnBoard's crime index is primarily based on the Federal Bureau of Investigation's Uniform Crime Report. It assigns a value of 100 to the national crime risk average. A higher value does not mean a place is not safe, but that it has higher crime risk than the national average. Since crime jurisdictional boundaries and ZIP codes do not always match up, risk for ZIPs is modeled based on the crime risk for the larger area.

OnBoard's education climate index (where 0 is "not classified," 1 is "low" and 5 is "high") is a measure of socioeconomic status for a ZIP code. Based on the Census Bureau's Socioeconomic Status measure, it helps identify ZIP codes with the best conditions for quality schools.

OnBoard obtains weather data from official National Oceanic and Atmospheric Administration weather reporting stations and assigns weather conditions through geographical modeling to appropriate ZIPs.

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