Drop down search categories, then search sub-categories.

I am interested to know how I might show in a row some drop down lists.

My website categories are defined by “continent” with subcategories of each continents “country” and then “state” or “district”.

I would like, if possible, for someone to have the ability to first select the continent of choice, then see in the next drop-down the countries that are sub-categorized to the continent of selection – and so on with state and district.

Then the visitor selects “search” or “go” and the results for that narrowly selected category shows up.

Any way?