6 7 The severity and frequency of wildfires have risen dramatically in recent years, drawing attention to the 8 term ‘wildland-urban interface’ (WUI). WUI refers to the region where man-made constructions meet 9 wildland vegetation. Existing conterminous United States (CONUS) WUI mapping methodologies were 10 based on the intersection of the area of wildland vegetation and houses, rather than taking into account the 11 direct physical contact of their boundaries. We mapped WUI in California (CA) based on the intersection 12 of these boundaries using building footprint data rather than census block data and thus obtaining a finer-13 scale mapping. It is a point-based approach for WUI mapping and therefore, does not require accounting 14 for the housing thresholds within a census block. This direct intersection of the housing and vegetation 15 polygons is referred to as a direct WUI, whereas the intersection of the two polygon boundaries at 100 m 16 is referred to as an indirect WUI. The linear WUI is a new WUI mapping that combines both direct and 17 indirect WUI. We selected wildland vegetation polygons using NLCD 2016 data and Microsoft building 18 footprint data for housing information. We chose shrubland, grassland, and woody vegetation types under 19 the category of wildland vegetation. Our findings demonstrate that the direct WUI is less fragmented and 20 has a slightly shorter length of 119,640 km than the indirect WUI (222,669 km) for the state of California. 21 More fires were ignited closer to direct WUI than indirect WUI due to their proximity to communities. 22 However, the overlap of past fire perimeters with indirect WUI is greater than that with direct WUI which 23 shows that although more fires ignited in the direct WUI, they burned more areas in the indirect WUI due 24 to embers transported by strong wind gusts during large wildfires. The study’s findings will help land 25 managers and policymakers in controlling fire dangers, planning land use, and reducing the threat to fire-26 prone communities. 27 Plain Language Summary 29 In this study, we mapped linear WUI and defined direct and indirect WUI for California. Direct WUI has 30 direct physical contact between flammable vegetation and housing boundaries and thus, has a higher risk 31 of fires due to human activities. While indirect WUI is mapped by the intersection of housing and a 100 m 32 buffer boundary surrounding flammable vegetation and therefore, has a lower probability of wildfire. 33 Results revealed that the direct WUI has a lower total length and is less fragmented than the indirect WUI 34 in California. However, a higher percentage of fires are ignited in the vicinity of direct WUI because of the 35 greater extent of human activities as compared to indirect WUI. Thus, even though direct WUI has a lower 36 total length in California, it has a larger potential of fire ignitions in its proximity to historical sites of 37 wildfires. 38