The implementation is simple
.script/plugin install firstname.lastname@example.org:abhishekpshukla/city_select.git
I have implemented it using jquery.
. "#user_state" is the dropdown list which contain the list of state name(I have consider the value of user_state as a FULL STATE NAME(for e.g. "Maharashtra") instead of STATE CODE).
Make a render file let say _city_select.erb and inside the controller render the _city_select.erb file and parse the selected state
Feel free to add a city if I am missing one.