Portfolio.com and bizjournals set out to identify America’s wealth centers, the most affluent cities in the nation. Here are the details:

Goal: The study’s objective was to find municipalities that have the earmarks of affluence, notably high incomes and expensive houses.

Places: The study covered all 420 cities, incorporated towns and census designated places that had populations above 75,000 and were included in the 2008 American Community Survey. (Census designated places are unincorporated areas that, in the opinion of the U.S. Census Bureau, possess all of the other characteristics of cities.) The study group ranged in size from New York City, with 8.36 million residents, to Camden, New Jersey, with 75,456. All statistics are for the cities alone, and do not encompass suburbs or other communities within their metropolitan areas.

Source: All raw statistics were collected by the U.S. Census Bureau as part of its 2008 American Community Survey, which was released in late 2009. All percentages were calculated by Portfolio.com/bizjournals.

Factors: Portfolio.com/bizjournals used a six-part formula to determine the relative affluence of each city. These were the factors:

1. Per capita income, which is defined as the average amount of money received by each resident of a given area in a given year. It encompasses such diverse sources of income as salaries, interest payments, dividends, rental income and government checks.

2. Median household income. A median is a midpoint, with incomes in half of a city’s households being higher, and half being lower.

3. Percentage of households with annual incomes of $200,000 or more.

4. Upper 20 percent threshold for household income. This is the point that is higher than 80 percent of all incomes within a city, but lower than the top 20 percent.

5. Median home value. (If the median was higher than $1 million, the Census Bureau reported it as $1,000,001.)

6. Upper 25 percent threshold for home value. This is the point that is higher than 75 percent of all home values within a city, but lower than the top 25 percent. (If this threshold was higher than $1 million, the Census Bureau reported it as $1,000,001.)

Adjustments: The formula adjusted factors 5 and 6, converting each to a ratio of home value per $50,000 of median household income. This step dampened the impact of any housing bubbles that might have overinflated property values in upper-income communities. (Home values listed on the chart accompanying this study are actual values, not the adjusted ratios.)

Scoring: Each city’s statistics were compared against the study group’s averages in all six categories. Above-average dollar figures or percentages received positive scores, while below-average results received negative scores. Each city’s six category scores were totaled to determine its overall rank. Final scores ranged from 22.759 points for Newport Beach, California, to minus-12.188 points for Reading, Pennsylvania.

(Read the full story about U.S. wealth centers by clicking here and explore an interactive map of the United States by clicking here.)