Get shipping fee in cart without zip code

I want to generating shipping rate for the cart. I find an API for generating it in this page:

Generate shipping rates

It is

POST /{locale}/cart/prepare_shipping_rates.json

and

GET /{locale}/cart/async_shipping_rates.json

But API’s params need location infor in detail like: zipcode,…

However, when I set shipping zone in setting, I’ve just seen the general location like market, country without detail information like zip code. So I wonder that why the API need detail information as input. What is it used for? Is there any way to get the shipping fee what is use only country without zip code or other information as well?

If anyone know the answer, please let me know. Thank you in advance