There's more than one way to define who lives in a wildfire zone.

The Colorado State Forest Service uses its "red zone" as a guide to analyze the areas of greatest risk - and highest firefighting priorities - when a forest fire erupts anywhere in the western half of the state. Terrain, forest conditions and housing density all figure into its formula. The red zone includes a buffered area of potential damage, averaging 2 miles wide, around places where a catastrophic fire could occur.

With the Forest Service's definition and U.S. Census Bureau data, Denver Post computer-assisted reporting editor Jeffrey A. Roberts used geographical information system (GIS) software to calculate the population of the red zone and break down that population by county.

Two experts provided technical assistance to The Denver Post: Skip Edel, GIS program manager for the Forest Service, and Dave Theobald, a research scientist at Colorado State University's Natural Resource Ecology Laboratory.

Responding to questions from The Post, Theobald did a separate population analysis, counting only those people who live in forested areas or within a half-mile of them, rather than in the entire red zone. Under that narrower definition, which excludes urban areas such as downtown Boulder, Theobald found 464,854 people in 2000, up from 331,236 in 1990.

Jefferson County estimates that 63,000 people live in the area it regulates as a wildfire zone. The Post's analysis of the Forest Service's red zone shows 147,000 Jeffco residents in areas vulnerable to wildfires.