Scientists interested in minimizing numbers of slums globally have reported a way to diagnose city spaces as slums and solve access problems inherent to these complex urban spaces. Their approach is designed to transform these informal neighborhoods, characterized by a lack of access to necessary urban services, into formal city blocks. The researchers' underlying optimization algorithm, already in use in several locations, will provide a useful tool to governments and nonprofits focused on solving critical development problems in fast-growing locations in many developing nations. Currently, four billion people around the world live in urban areas, and of these, about a quarter of them live in slums. Slums vary in their physical appearance and layout, but they all lack addresses (making them hard to study) and access to essential services, such as water and sanitation. Urban planning experts have attempted to better design cities to avoid slum scenarios; however, the ideal city blueprint has remained elusive. Here, Christa Brelsford and her colleagues assembled a diverse set of urban maps from around the world and used two categories to analyze the topography of the related urban spaces. They analyzed the spaces either by access to systems (such as roads and streets) as well as by the types of structures they included (buildings and public spaces). This allowed the researchers to describe each location as a connected set of blocks. Urban slums are characterized by a series of disconnected places, they say. Missing infrastructure could be put in place at minimal cost in such locations, their approach shows, to connect specific informal neighborhoods - a process known as "reblocking." The framework introduced in this study is currently being applied to slums in Cape Town and Mumbai in which neighborhood communities and respective governments are working together to map informal settlements of the cities and produce reblocking proposals that are in line with their unique preferences, priorities and budgets, Brelsford et al. say.