The advantage cities have after the collapse is that you dont need to bury the dead they are already self contained in their concrete tombs
, only joking actually. I have seen in recent years some pretty natty urban prepper set ups with stuff like roof top gardens and veg plots, multi building rain capture systems, indeed one building in the states ( or Mexico) has one big heat exchanger driven by sunlight and it creates a humid environment that you can grow tropical foods in. We cannot write cities off completely but theres no avoiding the fact they have a much harder task to face during the initial die off period. But I do think a very hard effort by a conscienious urban prepper or group in plotting and identifying useful assets could create a small scale self contain community in a city.
I like the growth of city garden coops like the ones in places like Walker and some housing coops refurbishing former terraces into modern eco homes with good sized community gardens and allotments, if the will is present in the preppers is the REAL issue.
For example if a prepper is adamant he is NOT going to relocate out of the city for whatever reason, then surely to offset that it must make sense for that urban prepper to live in a house with a decent sized garden so they can part grow their own food, live in a house with a south west facing aspect so they can harvest solar energy, live in a house that can be secured, live in a house with plenty of storage etc etc that way at least they would not need to rely on luck so much.
And no this is not an attack on oppressed urban preppers its just open thinking and pushing forward sensible debate.