Hello, 

In order to do this, you need to go in the contacts’application > configuration > country. Then, select the country you want and thick the box “Enforce cities”. 

After that, you can import the cities, zip code and state on the model res.city by clicking on the smartbutton “cities”.

Now, when the country “France” is selected while creating a contact, if you type the zip or the city, your dropdown list will get shorter and when selecting the right city, the zip and state will be filled in automatically. 

If your client always creates contacts coming from the same country (for example “France”), you can set the “France” as country by default and it will reduce even more the risks of error of creating cities with no country selected.

~credits to NIVA~