Can crowds map war? Crowdsourcing wartime territorial control maps from Wikipedia

Who controls territory during an armed conflict, and how does that control shape the course of the war? Wartime territorial control is central to theories of armed conflict, yet cross-national data on control are coarse, static, or limited to single cases. We introduce a new dataset of overt territorial control---which armed group openly holds each town and military site---built from crowd-sourced Wikipedia conflict maps. These maps mark towns, villages, and military sites with icons colored by the faction that controls them. We scrape the full revision history of 20 such maps, roughly 35,000 revisions tracking some 25,000 locations across 45 state-based armed conflicts since 2014, and reconstruct which group held each point on each day and whether it was contested. Our data agree with expert-coded Carter Center maps of Syria in 90 percent of settlement-months, and the Wikipedia map of Ukraine agrees with two professional trackers of the war in 98.5 percent of place-days. Our validation effort also allows us to report which features of the data are most and least reliable. An accompanying R package provides helpful tools for aggregating and standardizing control into panel data.