3D city models can be created using a variety of techniques, including Aerial Photogrammetry and Extruded Buildings Footprints. Extruding buildings footprint polygons is usually the fastest, most cost-effective way of creating a 3D city model. These 3D maps can give a better understanding of the as-built environment than 2D maps. However, the resulting 3D city model is often too generalised, with many important features omitted or simplified.
This lack of detail can result in a city model with many errors, clearly visible when we compare this model to a photogrammetry-captured model. See below for a direct comparison between a 3D model of Cardiff generated by extruding buildings footprints and AccuCities 3D model of Cardiff.