In smart cities, diverse modes of transport coexist, making the integration of multimodal networks essential. However, existing approaches typically simplify modal transitions into single points, which does not fully reflect real-world. To overcome these limitations, we propose a data model that represents mode transitions in three-dimensional space. The proposed model defines the transition between different transport modes as a 3D transfer space to represent internal routes in detail, and integrates the networks between individual transport networks through this space to form a unified multimodal transportation network. This approach enables precise modeling of transfer paths across micro-scale spaces and allows for the flexible integration of individual transport networks without requiring modifications. We expect that the proposed model will effectively address the demands of multilayered transportation environments and serve as a foundation for developing human-oriented multimodal navigation systems.