Presently a very large number of public and private data sets are available around the local governments. In most cases, they are not semantically interoperable and a huge human effort is needed to create integrated ontologies and knowledge base for smart city. In this paper, a system for the ingestion of data for smart city related aspects as road graph, services available on the roads, traffic sensors etc., is proposed. The system allows to manage a big volume of data coming from a variety of sources considering both static and dynamic data, these data are then mapped to a smart-city and mobility ontology and stored into an RDF-Store where this data are available for applications via SPARQL queries to provide new services to the users. The paper presents the knowledge base and the mechanisms adopted for the verification, reconciliation and validation. Some examples about the possible usage of the knowledge base produced are also offered and are accessible from the RDF-Store. Keywords Smart city, reconciliation, validation and verirication of knowledge base, linked open graph.