Obtaining geocoded electoral results at precinct level can be challenging in many countries. In this study, we present two validated methodologies developed to overcome these difficulties, and we build new geocoded electoral results for several Italian cities. Our dataset covers the last 20 years (1999-2022) and includes data for various types of elections, including national, regional, municipal and referendum. We provide an overview of some notable patterns in voting trends in major Italian cities. These include a high level of heterogeneity in voting within cities, an increase in spatial polarization of voting behaviour, and an increasing concentration of left-wing voters in central and wealthier areas of metropolitan cities. These trends may be influenced by a range of factors and can have significant implications for political representation and policy-making. Our dataset provides a valuable resource for understanding these trends and exploring their underlying causes.