Over the past several months, the epicenter of the COVID-19 pandemic has shifted from China to Italy to the United States. One way to spatially visualize this shifting gravity of the pandemic is by using an idea and method from Quah (2011) to track how the center of gravity of a particular variable is shifting over time. In particular, we can locate all COVID-19 deaths recorded at a given day according to their location, find the average location, and project this point ("the center of gravity") to the earth's surface. Quah (2011) used this method to show how the center of gravity of global economic activity has shifted from Europe to China over the past decades. The method has since been used to show that the center of gravity of global poverty is shifting towards Africa. Applying the method to COVID-19 deaths using data from Johns Hopkins Coronavirus Resource Center allows for tracking the epicenter of the pandemic over the past months.
Doing so reveals that the center of gravity moved from China in February, to Italy in March, and towards the US in April. In the last month,Increased cases in Africa, the Middle East and South Asia are further exacerbating this trend.
The map has some important caveats, however. Firstly, supposing half of the case deaths are in Brazil and the other half in Russia, and there we no cases anywhere else, then the center of gravity would be somewhere between Russia and Brazil, probably in Northern Africa, despite this region not seeing any cases. The center of gravity makes most sense when, at a given time, the majority of cases are concentrated in one region. Secondly, since we only use country-level data, we place all daily deaths at the geographical midpoint of a particular country, meaning that the map neglects important subnational spatial patterns. Finally, to the extent that deaths go uncounted in certain countries, the center of gravity could be impacted.
Despite these caveats, the center of gravity allows for a simple visualization of how the pandemic is evolving globally over time. There can hardly be any doubt that the pandemic is heading south, to parts of the world where health infrastructure and social safety nets too often are weak. In fact, The World Bank Group is ready and engaged with emergency response efforts around the globe.