Wildland-urban interface

The wildland-urban interface, often shortened to WUI, is the area where human development meets or mixes with wildland vegetation. It describes a geographic relationship between development and surrounding land. A mapped WUI boundary depends on the definition, land-cover information, and housing data used to create it.

Interface and intermix

The National Institute of Standards and Technology distinguishes development beside wildland vegetation from housing dispersed among it. These are commonly called interface and intermix settings. NIST also explains that broad WUI categories do not capture every detail relevant to fire spread between individual properties. NIST WUI definitions.

This makes the term useful for understanding community conditions while leaving room for more detailed assessments. A broad map category and a specific property's circumstances answer different questions.

Example

Hypothetical: A county map identifies a neighborhood beside a large area of wildland vegetation as WUI. A second mapped area contains homes scattered among similar vegetation. The legend distinguishes the two development patterns.

The map helps describe where development and vegetation meet. It does not say that every home has the same exposure, that a fire is currently present, or that a particular building will be damaged. Those claims would require different information and a clearly stated assessment method.

Common confusion

WUI is not a synonym for an active wildfire boundary or evacuation zone. Those maps describe a specific event or protective action and can change on a very different schedule.

It is also not automatically a parcel-level risk rating. Two properties within the same broad category can have different surroundings and building characteristics. Conversely, a line on a general map should not be read as a guarantee of safety for properties just outside it.

Reading a WUI map

Check the publication date, geographic scale, and definition. NIST's comparison shows that implementations use different housing, vegetation, and distance criteria. A map using one method may draw a different boundary from a map using another.

When comparing years, determine whether the observed change reflects new development, changed vegetation data, a revised method, or some combination. Report the number of homes, people, or acres only with the corresponding measurement unit and source year. An increase in mapped WUI acreage alone cannot establish an equivalent increase in population or fire incidents.

Related terms

• Vegetation fire
• Structure fire
• Geographic information system
• Boundary change

Sources

• NIST: WUI Definitions — Updated August 25, 2023; explains interface/intermix concepts, differing map criteria, and limits of broad categories for individual properties.