Anyway... since the revamp the encampment is a bigger production gain than an IZ, once you are under a factory zone already.
That depends on adjacency bonuses. Also, remember an Encampment isn't providing maximum production until it has an Academy, which is Industrial era, whereas a even a non-Factory IZ gets its benefits on the same tech. Craftsmanship is in the same Era of Civics too.
So lets assume we're in the Medieval era. We can build either an IZ or an Encampment (say, perhaps the city has already built its CH). Say you can get +2 production from the IZ adjacency. Then its +4 production from the IZ versus +3 from the Encampment. Now add craftsmanship, now its +6 production from the IZ versus +3 from the Encampment. If that city could only get +1 production for the IZ from adjacencies (say, from building it next to two other districts), then that becomes even for the Encampment (which means you should build the Encampment because it has side benefits the IZ does not have). Craftsmanship ups that to +2p, leaving us at +4p versus +3p and the other Encampment benefits. I'd say 1p extra versus the Encampment might still be worth building the actual Encampment, but its situational (like if it will help with strategic resources, or if you have a lot of Industrial or Military CS's, or what type of victory you are going for).
Now lets say we're in the Industrial era. Same situation, either an IZ or an Encampment. Assume the city is also already covered by another Factory, so we won't build one here. IZ gets +2 from adjacency, and +2 from workshop and +100% adjacency from craftsmen for 6p. Encampment also gets 6p (Barracks+Armory+Military Academy) and 2 housing but is a bigger investment (unless possibly using Veterancy, which should be explored further).
Looks like if you don't need the Factory in the Industrial era, or if you can't get very high adjacency bonuses for your IZ in the Medieval era, then you should probably build an Encampment.
lots of production from non-mine/quarry tiles (pastures, rainforest resources, etc.)
+
no mines or quarries for IZ adjacency bonuses
+
covered by another city's factory
=
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optimal location for an encampment district
Pretty much this.
City States are a big X factor in this decision too. If you are playing a heavy military game, and you have a lot of Military CS's, that might lean a bit more to Encampments. If you have a lot of Industrial CS's and are more interested in peaceful expansion, the IZ is better. More production for building districts and buildings is a very powerful bonus.
I'd still say that you should probably build your CH first. Trade Routes providing just as much production, but also food and gold (from the CH adjacenies) and being able to place them in any city you want just swamp the Encampment (and pretty much everything else).
I'd also consider placing your victory district before an Encampment, although it might be better to get the boost in production first.