Nowadays, cities face complex environmental urban challenges while simultaneously being responsible for 70% of global carbon dioxide (CO2) emissions. District approaches, such as positive energy districts (PEDs), offer great potential for primary energy savings and CO2 emission reduction compared to individual decarbonization of buildings. A PED is an area of more than three buildings that, through renewable energy sources and energy efficiency, generates more energy than it consumes. However, the absence of energy performance standards and tools tailored to assess these district-based concepts impedes its wider implementation. Ontologies, understood as formal, explicit, agreed representations of a specific domain, can help address this issue by providing a standardized way to organize the data. Thus, this article aims to create a preliminary basis for evaluating urban districts’ energy and CO2 performance, thereby enabling a more comprehensive analysis of decarbonization pathways. A data model district case study in Latvia will be used to demonstrate it. All the data is organized and matched in an ontology structure to develop a systematic framework for assessing different indicators within district contexts. By employing ontologies in this context, the study seeks to demonstrate the potential of ontologies to enhance the assessment of district studies.