The problem of identifying functional regions in an urban setting has been approached in literature using two general methodologies: top-down, encoding expert knowledge on urban planning and design (e.g. into patterns) and using that knowledge for identification, and bottom-up, relying on crowdsourcing and Volunteered Geographic Information (VGI) to train learning models, using techniques such as Latent Dirichlet Allocation (LDA) topic modeling. Both approaches have their advantages but also face important limitations, with knowledge-based approaches being criticized for scalability and transferability issues and data-driven approaches for lacking interpretability and depending heavily on data quality. To mitigate these disadvantages, we propose a novel framework that fuses data and knowledge in three different ways: functional regions identified from individual approaches are evaluated against each other, knowledge from patterns is used to adjust learning model results and topic models are used to adjust pattern-based results. The proposed methodologies are demonstrated through the use case of identifying shopping-related functional regions in the Los Angeles metropolitan area. Results show that the combination of results from knowledge-based and data-driven techniques can help uncover discrepancies between the two different approaches and smoothen inaccuracies caused by the limitations of each approach.