How to represent relationship between geographical locations like Countries, States, Cities, Towns and Areas into classes?

I want to create a global level database for GeoMap Service and want to represent them through Entity classes along with their relationships.

How I can have such entities classes with their relationship.

World have Countries, Country having States, State having Cities, City having Towns and Town having ZipCodes.

I want to have such complex queries request in system that I need to serve, like below

1. Get List of 4 countries with their State Data.
2. Get List of 4 States with their Towns Data.
3. Get List of 4 Counties with their Towns Data.

Suggest some references if you have any.