[Mr.Monkey]

Just type something like: "zip code of [you locality], [your city], [ your state]"

But it's just a bit weird that you don't know your zip code (even if it's available in your country or not).

Not all countries use/utilize zip codes, nor sometimes they are common knowledge. Here in the US, apart from the regular 5-digit zip code, there is an extension to it for more localized sorting (I suppose). Normally, people use the 5 digit string, but sometimes the extention is needed.

In other places, such as the other side of the border from the US, in Mexico, instead of the common usage of zip codes/ing they rather associate areas based on "county". As like, this place is closer to said bigger urban area, thus associated with that. Its more or less consolidating what they can associate/mark certain regions where there might be less people living there or none.