If I recall correctly, in at least some of the Caesar/Pharaoh/Zeus/Emperor games, access to workers is a binary "Did a worker walk by here recently?" check, and if the answer is yes, then the whole city's population of workers is available to the building. So to serve a remote cluster of mines or whatever, you can have a "slum" that's one or two houses big.
There might be seven or eight levels of "common" housing that provides workers and then two or three of "upper class" housing that doesn't. But at least to me, a block of insulae isn't a "slum" in the game--a couple of huts with no water or food are.
Sim City btw, does the same thing with Residential / Commercial / Industrial zones. All "traffic" start from a residential zone, then goes to a industrial zone, and finally ends in commercial.
That means a singular tile of "Residential" zone can "feed" the entire industrial sector. While a singular "Commercial" tile can serve as where the industry drops off their goods.
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So I knew that fact for Sim City (and took advantage of it in some designs). I never really knew that for Caesar / Pharaoh.
There might be seven or eight levels of "common" housing that provides workers and then two or three of "upper class" housing that doesn't. But at least to me, a block of insulae isn't a "slum" in the game--a couple of huts with no water or food are.