This study proves that the need to assess and enhance urban sustainability becomes vital. The implications are relevant to the constant urbanization and technological progress, which calls for sustainable smart city development. On the grounds presented above, we offer and describe the model to measure and evaluate urban sustainability through SCIs. Calculations performed on the model differ across the total of 102 cities worldwide, ensuring quick and effective calculation and visualization. The model on which calculations are based uses six indicators, which are mobility, environment, government, economy, smart people, and smart living. The rationale provides an opportunity to analyze and interpret data regarding the indicators, which makes the calculation of SCI (Smart City Index) by city for each indicator possible, as well as conclusions concerning major strengths and focus areas for improvement. The obtained results are presented through promising data visualization techniques to make SCIs intuitive and enable the comparison of cities. The findings demonstrated large variations among smart cities, which points to the necessity of developing targeted policies and investments. With these contributions, we are confident that the paper will make a valuable addition to the existing knowledge and provided further guidance and recommendations for the stakeholders involved in a sustainable urban environment.