In model transformation, the population of attributes on the target side constitutes the last step of the conversion process that carries over that part of the input which is often perceived as the most valuable actual information. We are employing a graph-based model transformation approach to convert building information models into geospatial city models. In this paper, we are reporting on different types of transformation rules to populate the attributes on CityGML side using information extracted from the IFC data. We document the various ways how attribute values can be stored in IFC and CityGML respectively and identify patterns that bridge these endpoints in the conversion process. These patterns lead to a set of prototypical graph transformation rules which have been applied to a range of building projects. The novel graph-based approach to IFC-to-CityGML conversion implicates an intuitive visual representation of these rules. This work can also serve as a starting point to convert IFC data to other formats or to populate CityGML from other data sources.