District heating networks (DHNs) are key to energy transition strategies, offering cost-efficient, reliable and sustainable thermal energy distribution. However, obtaining realistic and efficient designs in dense urban environments is a demanding task. Critical factors like optional user connections, field constraints, multiple production scenarios, and thermal-hydraulic viability are often overlooked in typical engineering approaches. To overcome these limitations, a planning tool integrating graph theory, mathematical optimization, and thermal-hydraulic simulations was developed. The problem is solved through selecting consumers from prospects and computing optimal layouts, pipe diameters, and consolidated costs. Flow velocity regimes, demand diversity and temperature regimes at substations are included. A thermal-hydraulic simulator concurrently validates performance for considered scenarios. A realistic design case based on available data is presented, exhibiting in particular the impact of the chosen maximisation objective on results.