This is a protocol for sampling people in order to understand patterns of mobility and activity-space segregation at the scale of city-days. The goal is to obtain a representative sample of the space-time paths that exist in a given city. Sampling points and times are choosen and then used to recruit participants. If participants consent to be part of the study, they (1) respond anonymously to a survey about their activity-spaces, and/or (2) use a mobile phone application to track themselves during a 1-week period and share their anonymized trajectory information with the research team. This protocol has been developed thanks to funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 657956.