House prices around the Washington area kept climbing last year, mirroring the seemingly unstoppable national housing boom that has continued despite weakness in the rest of the economy.

The median sales price for single-family houses and townhouses in the region rose 16.5 percent last year from the year before, increasing to $240,000 from $206,079, according to a Washington Post analysis of government sales records. (For a Zip-code-by-Zip-code analysis of these results, see the maps and charts throughout this section.)

Despite widespread speculation that the housing price rise here and nationally could be a bubble getting ready to burst, there's no evidence of falling prices in these numbers.

The steepest increase came in the District of Columbia, where the median price rose a stunning 33 percent to $250,000 from $187,900. The pace of gentrification and the squeeze on low-cost housing have become political issues in the city, which only a few years ago was dealing with worries about falling property values as tens of thousands of residents fled to the suburbs.

Other close-in jurisdictions saw dramatic jumps, too, with median prices in Alexandria rising 25.9 percent and those in Arlington increasing 18.9 percent.

Alexandria was the jurisdiction with the highest median price, $365,000. Prince George's County had the lowest at $165,000.

The median price is the point at which half the prices are higher and half the prices are lower.

The analysis covered 13 counties and cities and a handful of small independent jurisdictions in an area stretching from Loudoun County in the west to Anne Arundel County in the east, and from Frederick County in the north down to Charles and Prince William counties in the south.

The analysis excluded condominiums. It also excluded sales of commercial buildings, unimproved land and other nonstandard transactions.

Because of geographic variations, these numbers are not strictly comparable with past Washington Post studies or with other price studies. For instance, the Office of Federal Housing Enterprise Oversight recently said that prices in the Washington area rose 11.3 percent last year, but that survey covered a larger Census-defined area that stretches into West Virginia.

Still, the trends are much the same. For example, the National Association of Realtors found that median prices rose 17 percent in the Washington area in 2002, to $250,200. That study looked only at existing houses and used the expanded metropolitan area definition.

In The Post study, median prices rose in every jurisdiction examined. The smallest increase was in Charles County, where the median price rose just 0.6 percent.

Of note is how few Zip codes in The Post study actually registered a drop in median price. In the District and Fairfax County, not a single Zip code experienced a price drop.

Shifts in median price are affected not only by price appreciation, but also by shifts in the type of housing purchased.

In almost all the Zip codes with falling prices, the logical explanation is that buyers opted to purchase smaller houses, rather than that individual houses actually lost value.

Median prices are an unreliable measure when comparing a small number of transactions. That effect shows up in several Zip codes that have dramatic price swings but few transactions. Those results are probably not meaningful.