Integrating multiple data sources is challenging due to differences in data formats, structures, and quality. Data visualization consultants must first establish data connections and ensure consistent data formatting. This often involves using ETL (Extract, Transform, Load) processes to clean and combine data. They must also handle data refreshes and ensure that integrated data is up-to-date. Addressing discrepancies between data sources and aligning them with a unified data model is crucial for accurate visualizations. Effective communication with data owners and a strong understanding of data integration tools like Power BI, Tableau, or D3.js are essential to tackle this challenge.