Therefore, there's no problems with most characters starting out, at least, in Pandemonium City. See the realm maps for positions of the more major Ruins.
Most capitol cities are the only sources of population in the Realms.
Natural resources are scarce in Hell. Wood is a commodity in Hell, with more important uses than mere building, so the Damned serve in that regard as well. This fact may lend support to the ancient Giant legends that Hell was, for a very long time, a Paradise of plant and animal life, before the inexplicable death of Hell, before the Fallen arrived. Many of the Cities, ruins, and most of the Middle Tiers of Pandemonium City are constructed not only out of brick and rock, but also the frozen, contorted and petrified bodies of fully-mature Damned. How these fully-developed Damned end up degraded this way isn't known, at least to common knowledge.