Planning for elections, calculating numbers living in poverty, the denominator in disease incidence rates, assessing natural disaster impacts, measuring demand for services—underlying all of these activities and countless more is the need for ongoing subnational scale data on population sizes and characteristics. In many high-income countries with well-documented censuses, comprehensive civil and vital registration systems and a wealth of other ongoing surveys and registers, it is often taken for granted that fine-grained, robust, consistent and recent data on populations are readily available. While there is growing capacity in low and middle income countries, obtaining consistent, comparable and spatially-detailed demographic data can be a challenge, particularly in the most conflict affected and fragile states, where it can be decades since the last census. Professor Tatem will present an overview of the work of WorldPop (www.worldpop.org) in developing methods to complement traditional data sources with those from satellites, cell phones, social media and GPS-located surveys and build more spatially detailed and regularly updated population data. He will describe the methods and models used to integrate these data within WorldPop and beyond, and how the outputs are finding use within governments, UN agencies and many others organizations to support development and the improvement of health.