That matters because government planners use maps to analyze the city. They identify where the population lives, and they shape plans for public services and investment based on that information. If settlements are not mapped, they don’t exist in the eyes of the state. Worse, the people who live in the low-quality, self-built housing I detected at the periphery tend to be more marginalized already: often lower-income residents and migrants to the city. They are also more often located in geologically vulnerable areas that are at risk of natural disasters such as flooding and mudslides. Satellite images are useful for urban planning, but relying on the information they provide without verifying conditions on the ground can cheat the world’s most vulnerable populations.

The interface between technology and unequal social structures is finally getting some much-needed attention. When smart-city institutions rely on computer algorithms to expedite their work, they can embed unintended bias into municipal operations, resulting in things like racially biased criminal sentencing, information searching, and financial access.

One of the reasons for this embedded bias is that human beings are the ones creating the code and they write it based on the assumptions in their own knowledge frameworks and experience about how the world operates and is organized. As designers learn about unjust and mistaken outcomes, one strategy for overcoming these blinders is to have a workforce with more diverse experiences and worldviews writing the code. Another is to have a more transparent and democratic process for correcting and improving them.

Algorithmic justice in urban planning has received less popular attention than criminal justice or surveillance. But the stakes are high for land use and city infrastructure, too. For the first time in human history, the majority of human beings live in cities. This historic shift has occurred because of rapid urbanization in the Global South, which has primarily been driven by the influx of rural migrants. Despite coming to cities with fewer resources, these new urbanites have helped fuel the urban economy by providing a large body of low-cost labor. At the same time, anti-immigrant sentiment has caused growing contestation of their right to be in the city, pushing newcomers to eke out livelihoods in precarious situations.

In Ho Chi Minh City, one-third of all jobs are in the informal sector. Traditional methods of counting such people—census questionnaires and field surveys, for example—are costly to administer and quickly outdated, since they are usually collected every 10 years. Furthermore those methods usually do not include the new urbanization that may occur just outside official urban boundaries. It’s difficult to count the new population of urban immigrants and their informal livelihoods when they are living outside regulatory bureaucracies and their documentation processes. The location and patterns of their settlements are often unplanned. As a result, some of the poorest residents are often living in precarious places without public sewer, drainage, solid-waste, and other infrastructure systems.