Forced displacement of human populations owing to conflict or natural disasters is very difficult to measure. During these crises, the traditional methods of assessing changes in populations - which mostly rely on surveys - are simply not possible. We chat to Dr Douglas Leasure from Oxford's Leverhulme Centre for Demographic Science about how his team have been using social media data to assess the internal displacement of populations in Ukraine since the Russian invasion in February 2022, in order to help ensure humanitarian aid is delivered as effectively as possible. If you would like to read the original research paper about Doug's work, you can access it here: 'Nowcasting Daily Population Displacement in Ukraine through Social Media Advertising Data'. You can find out more about the work of researchers at the Leverhulme Centre for Demographic Science in this Oxford Sparks micro-documentary: 'Demography: Understanding Our World'.