Defining cities and measuring what is urban shapes knowledge across fields. But delineations from what is rural and boundaries at the edges of cities or within them are not always harmonized across contexts or paradigms of study, a problem tackled in different ways across this issue’s content. What makes a city a city? Definitions of urbanity vary by country, region and institution. Many states and agencies define a city based on a population threshold, some define a city by administrative boundaries, and others integrate multiple factors — such as population density, land-use characteristics or economic activities — to build a more multifaceted definition. In recent years, the UN1, among others, have worked not to retire local definitions but to harmonize them across boundaries to enable meaningful comparisons. A persistent feature of defining what counts as urban is its opposition to the category of rural, although the distinction in many ways is mutually constitutive. As an editorial team, we are invested in growing Nature Cities into a generative place to flesh out how to define a city, the implications of different definitions and measures, and of urban–rural connections and dichotomies. Many of the works in this issue tease out aspects of these elements. In a World View, Batáry draws the conclusion that planning models must integrate cities and their rural surroundings to be sustainable. With a life shaped by both city and village life, Batáry considers how profoundly the landscapes of both have changed in post-communist Hungary, and yet how deeply they affect each other. The question of integration extends to the relationship between urban development and natural ecosystems within the city itself. In the case of Nusantara, the new capital city of Indonesia — planned to be a ‘forest city’ — the integration pertains to the city itself. In their