What are the essential characteristics of a federal Constitution?

A federal government establishes a dual polity, a two tier governmental system, with the Central Government at one level and the State Government at the other level. The federal Constitution marks off the sphere of action of each level of government by devising an elaborate scheme of distribution of legislative, administrative, and financial powers between the Centre and the States. A government is entitled to act within its assigned field and cannot go out of it, or encroach on the field assigned to the other government.