Is it possible to create this type of custom field? We need a field that holds assigned postal codes. Each Location entry will have this field and I'd like to have the following:


Buttons to assign postals by city, state, county (data grabbed from table I have)
on button click, the postal codes will be added to the actual field


I'm not sure if this is possible with a field or if I have to do this on a separate CP page

EDIT: I'll be more descriptive

We would have 4 buttons and 4 selects. The first select (State) will auto choose the state that the Location entry has on another field.

The 3 other fields (city, state, zips) will populate based on the proceeding choices.

So if the state is PA, the other 3 selects will populate only counties, cities, and zips located in that state.

There are buttons underneath each to assign either all zips in a state, county, city, or a single zip.

When they press add, I'd like to add to a table with the columns

State, County, City, Zip

I'd also like to have an option to add/remove assigned zips simply from a CSV in a textarea.

it sounds quite complicated, but I've done this exact thing on other apps...just not inside craft.
I don't fully understand it. But since modules can quite freely design their fields in the CP, this should be possible with a custom field type. 

It sounds to me like a variation of the select field.