The Lord Mayor's Annual Lecture, on 'Tomorrow's Cities', will form the opening keynote speech for the symposium on 'Measuring Cities'. It has been argued that economists mistakenly use nations as their unit of analysis when cities are the true generators of wealth. But many have struggled with the concept of cities as units of analysis. This symposium seeks contributions from those who study cities to define them, to specify the problems, and to suggest new analytical tools and techniques.