Isn’t going to have to cross unknown slum area (10)
I believe the answer is:
shantytown
'slum area' is the definition.
(shantytown is a kind of slum area)
'isn't going to have to cross' is the wordplay.
'isn't going to' becomes 'shanty' (I can't justify this - if you can you should give a lot more credence to this answer).
'have' becomes 'own' (to have something is to own it).
'to' says to put letters next to each other (I've seen this in other clues).
'cross' becomes 'T' (shape).
'own' after 't' is 'town'.
'shanty'+'town'='SHANTYTOWN'
'unknown' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for shantytown that I've seen before include "Area with ramshackle buildings" , "area of ramshackle housing" , "Deprived area of very poor housing" , "Deprived residential area" , "Collection of poor dwellings" .)