Federal wildland fire policy in the United States has been substantially revised over the past 10 years and new emphasis has been given to the wildland- urban interface (WUI), which creates a need for information about the WUI's location and extent. We operationalized a policy definition published in the Federal Register (US Department of the Interior [USDI] and US Department of Agriculture [USDA]), 2001, Urban wildland interface communities within vicinity of federal lands that are at high risk from wildfire. Fed. Regist. 66(3):751-777) to create national maps and statistics of the WUI to guide strategic planning. Using geographic information system analysis, we evaluate the national WUI by altering the definition's parameters to assess the influence of individual parameters (i.e., housing density, vegetation type and density, and interface buffer distance) and stability of outcomes. The most sensitive parameter was the housing density threshold. Changes in outputs (WUI homes and area) were much smaller than parameter variations suggesting the WUI definition generates stable results on most landscapes. Overall, modifying the WUI definition resulted in a similar amount of WUI area and number of homes and affected the precise location of the WUI.