Doesn't Boko Haram control basically all of northern Nigeria? Yes, it's incredibly rural (even deserted) but it's still half a country.
Not at all, even in the Borno state where Boko Haram and ISWAP are present, towns are controlled by the government, I don't think there is a single town that is controlled by Boko Haram/ISWAP right now.
Hardly. Northern Nigeria is majority Muslim. Most Muslims are not under Boko Haram control.
I believe this map shows the maximum area they controlled - and it was over a decade ago.
https://en.wikipedia.org/wiki/File:Wilayat_al_Sudan_al_Gharb...