This chapter studies the implication of aggregating establishments by categories with different levels of detail for modeling FTG. To this effect, the chapter conducts an assessment of freight trip generation (FTG) patterns homogeneity inside activity-based grouping. The method implemented is econometric in nature, which allows the assessment of the statistical significance of variables representing commercial activity sectors and sub-sectors. The results show that for some sectors 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.