This is a toy historical model, not a precise dataset. Each of 32 world regions carries hand-curated anchor estimates of the Christian share of its population at 19 moments between AD 33 and 2026, drawn from standard scholarship: Rodney Stark's early-growth estimates (roughly 40% per decade to AD 300), dated conversions (Armenia 301, Ethiopia c. 340, Rus 988), decline curves after the Islamic conquests, the colonial-era spread to the Americas, and modern survey figures (Pew, World Christian Database).
The simulation layer is a logistic growth plus diffusion model on a 2° land grid, seeded at Jerusalem in AD 33, spreading along populated cells, across narrow seas, and over dated ocean routes (1493 Atlantic, 1498 Cape route, 1565 Pacific). The blend slider mixes the two layers; at 100% history you see the anchor data, at 0% the model runs free under your parameters.
Heat intensity is the log-scaled Christian share multiplied by a population-density weight, so sparse deserts stay dark even where the faith is dominant, and early minority communities remain visible.