Want to add option in app for registration of adress.

Hi, I have app for delivery. Problem is that my developer add list of cities and user must choose one city from the list while he register new account. I asked him to make open option so user can add any adress and city by using google map. But he said its not possible and said:
«The list of city is the id of the user and driver the system based to this information and must be static, if user and driver able to enter this information manually the system will not understand the data»

Kindly let me know if you understand the issue and can solve this.

Thansk