This paper studies the implication of aggregating establishments by categories with different levels of detail for modeling urban freight trip generation. To this effect, the authors use a dataset of 2.970 establishments collected in 1998-1999 in France to conduct a formal assessment of FTG patterns homogeneity inside the traditional activity-based grouping (retail, manufacturing, wholesale, etc.). The results shows that, although, for some categories the traditional high-level aggregation includes sub-sectors with homogenous FTG patterns and thus produces appropriate models; in some other cases (e.g., retail, manufacturing), the sub-sectors have different FTG patterns and thus more detailed data is needed to calibrate accurate models. This research can be used to enhance the efficiency of data collection, as it identifies some sub-sectors that need larger efforts for data collection, and some other categories where FTG homogeneity allows for less detailed data collection without hampering the quality of the models.