In this episode of City Talks, Andrew looks at the economic theory of 'agglomeration' – the idea that the productivity of cities increases with size. The conversation explores the reasons why we see this phenomenon, as well as some of the misunderstandings that can arise when trying to measure its impact. Also touched on is the bearing agglomeration has on the Government's Northern Powerhouse initiative, the need to ensure that economic growth is inclusive, and how the vote to leave the European Union might affect urban policy going forward. Joining Andrew are Alexander Lembcke, Economist and Policy Analyst in the OECD’s Directorate for Public Governance and Territorial Development, and Henry Overman, Director of the What Works Centre for Local Economic Growth.