Context: The acceleration of infrastructure development presents many challenges for the mitigation of ecological impacts. The type, extent, and cumulative effects of multiple developments must be quantified to enable mitigation. Objectives: We quantified anthropogenic development footprints in a globally significant and relatively intact region. We identified the proportion accounted for by linear infrastructure (e.g. roads) including infrastructure that is currently unmapped; investigated the importance of key landscape drivers; and explored potential ramifications of offsite impacts (edge effects). Methods: We quantified direct development footprints of linear and ‘hub’ infrastructure in the Great Western Woodlands (GWW) in south-western Australia, using digitisation and extrapolation from a stratified random sample of aerial imagery. We used spatial datasets and literature resources to identify predictors of development footprint extent and calculate hypothetical ‘edge effect zones’. Results: Unmapped linear infrastructure, only detectable through manual digitisation, accounts for the greatest proportion of the direct development footprint. Across the 160,000 km2 GWW, the estimated development footprint is 690 km2, of which 67% consists of linear infrastructure and the remainder is ‘hub’ infrastructure. An estimated 150,000 km of linear infrastructure exists in the study area, equating to an average of ~1 km per km2. Beyond the direct footprint, a further 4000–55,000 km2 (3–35% of the region) lies within edge effect zones. Conclusions: This study highlights the pervasiveness of linear infrastructure and hence the importance of managing its cumulative impacts as a key component of landscape conservation. Our methodology can be applied to other relatively intact landscapes worldwide.