Who Held the Map? Twelve Centuries of the World in Flags, 800 to 2010, from Historical Basemaps and Wikidata

I combine the open historical-basemaps world maps (Ourednik and contributors) with flag and coat of arms statements in Wikidata to draw the world map at 30 dates from 800 to 2010, with each area filled with the flag of whoever held it at that date. The central problem is when not to show a flag: most polities flew no national flag before about 1700, many basemap areas are peoples or cultural regions rather than states, and Wikidata labels are ambiguous. I set out explicit rules: a flag is shown only when a Wikidata statement, dated by qualifiers or by the image's file name, covers the year, or when an undated flag belongs to a historical state within its lifetime and after 1150; otherwise a coat of arms, a plain colour, or a neutral style for peoples. Of 680 states, 535 (78.7%) matched a Wikidata item, covering 94.2% of the land they held. The share of the world's land that can honestly be filled with a flag in use rises from zero in 1000 and 3.7% in 1500 to 74.8% in 1900 and 97.3% in 2010. The largest single entry in the basemap is the Mongol Empire in 1279 (20.5% of the world's land); counting only the United Kingdom and its self-governing dominions, the British Empire in 1914 was larger (24.1%). European states held 4.9% of the land in 1492 and 46.1% in 1914, Russia included. For 93 of 194 present-day countries Wikidata dates the current flag; the median start year is 1986, often a re-specification rather than a new design. The results describe the basemaps and Wikidata as much as history, and I report their limits throughout. Interactive version: https://maps.tristanhotham.com/flags-through-time/. Data and code: https://github.com/Tristan-Hotham/flags-through-time. Blog post: https://blog.tristanhotham.com/2026/10/31/flags-through-time/. Licences: the paper (text and figures) is CC BY-SA 4.0, because the figures include flag images released under CC BY-SA. The simplified boundaries and area tables in the zip (data/maps, data/areas.csv) derive from historical-basemaps and are GPL-3.0. Flag images keep their own licences, listed in data/flag_credits.csv. Code is MIT. I wrote the text, with drafting and editing assistance from Claude (Anthropic), which also helped prepare the analysis code. I reviewed and checked all text and results.