I've seen a couple of mentions about a background count in Lagos. I can't find anything in Feral Cities about it, other than a couple of specific areas. Am I missing something?

Use your own judgment, I say. I'm running something in Sarajevo, and there is an encounter in the refugee camps - while I don't have any canon info, I'm going to rule that a 1-2 background count, only permitting the normal use of magic that is used to inflict misery or start conflicts.