1. A method comprising: by one or more computing devices, receiving, from each of a plurality of users, a posting request to a social networking system and a location associated with the posting request; by the one or more computing devices, assessing social and spatio-temporal proximity between or among a subset of the users based at least in part on the location associated with each of their posting requests; by the one or more computing devices, based on the assessment, creating a shared space for the posting requests of the subset of the users that are within a threshold spatio-temporal proximity; by the one or more computing devices, composing one or more content items from one or more of the posting requests of the subset of the users; and by the one or more computing devices, adding the content items to a dynamic list of content items associated with the shared space.