1. A method comprising: by the one or more computing devices of an online social network, accessing a social graph of the online social network, the social graph comprising a plurality of entity nodes and a plurality of edges connecting the entity nodes, each edge between two nodes establishing a single degree of separation between them, the plurality of entity nodes comprising: a plurality of place-entity nodes corresponding to a plurality of place-entities, respectively, each place-entity being associated with a particular geographic location, each place-entity having a place name comprising one or more n-grams; and a plurality of user nodes corresponding to a plurality of users of the online social network, respectively; by the one or more computing devices, generating a heterogeneous graph based on the social graph, the heterogeneous graph comprising the plurality of nodes and edges of the social graph and further comprising a plurality of n-gram nodes corresponding to a plurality of n-grams, respectively, wherein: each place-entity node is connected by one or more edges to one or more respective n-gram nodes, each n-gram node corresponding to an n-gram within the place name of the place-entity; and each place-entity node is connected by one or more edges to one or more user nodes, each edge between a user node and a place-entity node representing a social-networking interaction by the user corresponding to the user node with the place-entity corresponding to the place-entity node; by the one or more computing devices, assigning, for each place-entity node of a first set of place-entity nodes within the heterogeneous graph, an initial quality-score to the place-entity node; by the one or more computing devices, calculating, for each place-entity node of the heterogeneous graph, a final quality-score for the place-entity node based on the initial quality-scores of the first set of place-entity nodes, wherein the final quality-scores are calculated by iteratively propagating the initial quality-scores through the place-entity nodes, n-gram nodes, and user nodes of the heterogeneous graph until the sum of the quality-scores associated with the place-entity nodes, user nodes, and n-gram nodes reach convergence.