figure 5. Installing 300-mm main pipes across Aarhus Creek, 1955. (Source: Affaldvarme Århus; used with permission.) zones) for natural gas infrast ructures and district heating infrastructures. To en sure the most efficient heat supplies for the citizens, the zoning process compared the costs of natural gas networks, district heating networks, and individual household boilers within given geographical areas, and it ensured that heat from CHP plants and waste incinerators supplied local district heating systems via transmission systems. In short, zoning prevented internal com - petition between the two heat supply sources, it ensured a healthy economy throughout the heat supply infrastructure system, and that the figure 6. Ongoing construction. (Source: Affaldvarme Århus; used with permission.) 102 ieee power & energy magazine november/december 2021