## 5 Conclusions  
In this paper, we examined geometrical model-based thinking in organizing city logistics by use of cargo bikes, in the logistics system of shopping malls, primarily for Budapest. This solution seems to be a new approach, based on the results of the literature review. Nowadays, these cargo bikes are more and more popular, especially in Europe, but in America and in Asia, they are playing an increasingly more significant role in city logistics. Such research is very important not only because of the current city logistics challenges but because of their possible integration to smart cities as well. In the City Logistics Research Group of our Department [1], we are focusing on the so-called concentrated sets of delivery locations in our research project, and in this paper, we examined how cargo bikes can be used in their city logistics system based on the geometrical model of the logistics network. First, we presented the existing cargo bike-based systems and the related research results; next, our previous project was presented (from 2017). The results of this project gave the idea of this paper. In the concept, which was defined in this project, the CSDLs are divided into two groups: CSDLs on a central ring and CSDLs on rays, which start from the central ring, and we examined how to integrate the deliveries of the ones on the rays to the deliveries of the central ones. Figure 18: Application of the geometrical model-based approach. For this research, the previously used simulation model was developed further and extended to the whole of Budapest (with all its shopping malls) by examining several different concepts using cargo bikes. Based on the results, it was considered that with a relatively small extra investment (so, with a relatively small number of additional cargo bikes), a significant amount of goods and a significant number of stores could be integrated into the new system, while the delivery costs will increase only 20-40%, and we can exclude the potential negative effects of the traffic jams on the rays (as they can cause longer delivery times, with more delivery costs). It is also important that it is simpler to hire bike couriers nowadays, and there are not enough available, suitably qualified drivers for trucks and lorries, so it can be possible that the logistics providers will be forced to use more cargo bikes; in this case, this geometrical model-based approach can help to organize their deliveries. Next, the theoretical geometrical model, the symmetrical model, and the model of the real system were developed; with their graph theory-based notation, the description and application of such geometrical model-based solutions is an entirely new approach in city logistics planning. We applied this graph theory-based solution for the previously examined geometrical model in Budapest as a numerical example. In general, based on this geometrical model, it will be possible in the future to examine the suitability of given cities for implementation of the examined geometrical model-based new approach with cargo bikes. In the last section of the paper, the planned next steps of the research project were presented. The first and most important task is to define the reference structure. We gave the related plans based on the example of Budapest. It is assumed that the symmetrical model can be the reference one, but alternative optimal solutions must be examined as well. Next, we would like to develop a ranking model, which will be able to rank given cities after comparing them with their reference models. This ranking model will be able to decide about the suitability of the examined cargo bike-based city logistics concepts for given cities. The main result of this research project is the theoretical, symmetrical, and real geometrical model of the city logistics system of the concentrated sets of delivery locations, which provides an entirely new approach to the development of cargo bikes-based city logistics systems and gives the basis of our next research steps. Conceptualization, D.L.S. and K.B.