About 12,000 drow live in the City of the Spider Queen. The noble houses who run things occupy premium space along the corridors closes to the temple area (the spider's front legs, if you will). Social status declines as you get farther from the Temple, and those with no status at all live out beyond the Forum area entirely. The city area is about 6000 feet long and 4000 feet wide at the "legs." (Each hex on the map is 100 feet wide.) A normal medium-sized humanoid can walk from the Black Gate to the Temple stairs in about 20 minutes, not counting whatever time is spent being questioned by guards.
The Black Gate is the only official entrance into the city. It is guarded by a large contingent of experienced soldiers. The Gate itself has a permanent antimagic field built into it so that magical disguises and other devices cannot be used to gain access into the city. The guards, being drow, are of course immune to charm spells.
The Business Sector is where most outsiders conduct their business with the residents. It's a grimy, crowded area filled with crude stone buildings that act as storefronts, warehouses, and whatever else is necessary. Inns and flophouses provide temporary housing for those on extended visits and the lower classes of citizenry as well as non-drow have living quarters either within the sector or carved out of the walls on either side. Like many areas of Sheoloth, the outer canyon walls are honeycombed with high-density housing, somewhat like rowhouses but there are typically 3 levels of them with 2-3 floors each.
The Slave Pits house about 6,000 of the least valued slaves in prison-like conditions. The pit walls are lined with tiers of 12x18 cells with 4-8 occupants each and no doors to speak of. Drow guards patrol the upper edges and the floor below and put down any resistance or rough interactions before they get out of hand. Access and egress are by means of steel ladders. In addition to these slaves another 3,000 especially favored slaves (or domestic servants) are permitted to live with their owners. This is especially common with the noble houses, who own a large number of domestics.
The Inner Gate is a checkpoint intended to keep undesirables out of the Forum and adjoining areas. Non-drow are questioned as to their business by the guards at this gate and only those connected to, or on business for, one of the noble houses are allowed through.
The Forum is an upscale business district where drow go to buy food and provisions, equipment, entertainment, slaves, and pretty much anything else they need. Schools, libraries and government buildings are here and appropriately secured. Each of the wide corridors that stretches out from the Forum area, forming the legs of the spider shape, is a residential neighborhood. Hundreds of homes are dug out of the cave walls or narrow alleyways that radiate out from them, with each noble house owning a contiguous clusterof those homes. Less noble citizens live in the walls lining the Forum under cramped conditions, but they count themselves fortunate not to have to live out among the lowly folk beyond the slave pits.
The Temple Courtyard is a grand open area used primarily for public assembly. The stone is etched with a spider-web pattern with the nexus at the stairs to the Great Temple. Housing units carved into the Courtyard walls provide living space for favored clerics and VIP visitors to the city. House Clynestra also maintains a section of luxurious homes in this area, as Clynestra is the house of the Temple's highest officials.
The Great Temple of Lolth is carved into the canyon side at the very top of the courtyard. It occupies the entire space between the "antennae" of the spider and is a good 600 feet deep. The Temple rises five stories high and has smooth, highly polished walls that would be impossible to climb without some kind of magical aid. Atop the Temple is the lair of the Obsidian Dragon.
The secret passage the party is using to enter Sheoloth will bring you into one of the run-down housing units carved into the side wall of the Business Sector. The drow slave dealer who lives there is loyal to Nyrelda, though his neighbors may or may not be.