Hydrogen—and thus hydrogen transport—will play an important role in the German and European transition to climate neutrality. A German hydrogen transport network is currently being planned, but its appropriate structure and size highly depend on the spatial distribution of hydrogen demand and supply and their development over time. Moreover, the security of supply with both, hydrogen and natural gas, needs to be guaranteed during the transition period, as repurposing of the existing natural gas transmission system is a highly advantageous option for the building of hydrogen networks. Therefore, the integrated analysis of natural gas and hydrogen networks is a necessary and urgent, though complex, field of research. For this purpose, the article presents the database for the existing German natural gas transmission system (which in parts will be repurposed for hydrogen transport) and procedures for the development and evaluation of network topologies for both gases. The results for the German case show feasible development steps for the design of green hydrogen transport networks and the transition from natural gas in different scenarios. Open access to data and tools for technoeconomic assessment is provided.