About the data

Data and methods

The map combines very different kinds of evidence: medieval chronicles, ancient DNA and modern national surveillance. This page explains what each layer measures, how the map draws it, and what it cannot tell you.

Layers and sources

Plague: 6,846 locality-year records from 1347 to 1900 (Büntgen & Ginzler, EnviDat), plus ancient DNA evidence from Kara-Djigach in 1338–1339. Measles, cholera and paralytic polio: annual cases reported to WHO, via Our World in Data. COVID-19: WHO’s daily reported new cases, summed by year and by month. Monthly measles: WHO’s provisional monthly surveillance data from 2012.

Diphtheria, whooping cough, tetanus, yellow fever, rubella and mumps: official annual cases from the WHO/UNICEF Joint Reporting Form, 1980–2025 (rubella from 1997, mumps from 1999). Tuberculosis: WHO notifications of new and relapse cases, 1980–2024. These are notifications, not estimated incidence. Dengue: OpenDengue national counts from 1924 to 2025, monthly where published.

Full history and fine navigation

Full history shows one year at a time across the whole range, from 1300 to today. Fine navigation shows a ten-year window by month. Measles from 2012, COVID-19 from 2020 and dengue where published then use monthly values. Other diseases show their annual value for every month of the year. A country with no monthly report stays blank for that month. The map never falls back to its annual figure.

Colours and scales

Countries are coloured with fixed scales, so shades mean the same in every year. Historical plague counts documented records (1, 2, 5, 10, 25, 50 or more). Modern diseases count reported cases (1, 100, 1,000, 10,000, 100,000, one million or more). When a country has several diseases in the same year, it is striped. The stripes show that several diseases are present, not where or in what proportion.

Zero is not the same as missing

A reported zero is drawn in pale grey. No report is left dark. Missing years are never filled with older values, and infections are never estimated where no report exists. Reported cases are not all infections: they depend on testing, diagnosis and the willingness to report.

Borders and places

Modern borders are used as geographic bins, from public-domain Natural Earth boundaries. They do not represent historical states. Historical points are placed in countries by their coordinates. Points that fall outside any outline stay in the data but cannot be coloured.

Downloads and licences

Every processed dataset can be downloaded from the Sources panel on the map, along with an import audit that lists excluded rows and corrections. The plague derivative is published under ODbL 1.0. WHO-derived series remain under WHO’s terms. The data is a fixed snapshot taken in September 2026, not a live feed.

Sources

  1. Büntgen & Ginzler (2019) — Digitizing historical plague, EnviDat
  2. Our World in Data — Reported cases of measles (WHO data)
  3. Our World in Data — Reported cholera cases (WHO data)
  4. Our World in Data — Reported paralytic polio cases (WHO data)
  5. WHO — COVID-19 dashboard data
  6. WHO — Provisional monthly measles and rubella data
  7. WHO — Immunization data: reported cases of vaccine-preventable diseases
  8. WHO — Global tuberculosis programme data
  9. Clarke et al. (2024) — A global dataset of publicly available dengue case count data (OpenDengue), Scientific Data
  10. Natural Earth — public domain map data

More stories

How malaria disappeared from EuropeMalaria was once common from the English fens to Sicily and the Caucasus. How Europe reached zero local cases in 2015, and why the risk has not gone.How smallpox disappeared from the mapHow smallpox was erased from the world map, from the 1967 intensified campaign to the last natural case in Somalia in 1977 and eradication in 1980.The Black Death on a map: plague in Europe, 1347–19006,846 recorded plague outbreaks in Europe on a map, from the Black Death in 1347 to 1900: the worst years, the busiest places and why it retreated.