In the Preface to the 1855 edition of Leaves of Grass,Whitman describes how a writer can truly "belong" to his or her country. He argues that the first quality necessary in an American writer is a desire to become one with the land itself:

The American poets are to enclose old and new for America is the race of races. Of them a bard is to be commensurate with a people. To him the other continents arrive as contributions . . . he gives them reception for their sake and his own sake. His spirit responds to his country's spirit . . . . he incarnates its geography and natural life and rivers and lakes.

What does it mean to "incarnate" the nation's geography? Democratic federalism, Whitman's ideal political system, brought each state into an overarching union while allowing each to maintain its individuality. Glorying in the different topographical and cultural features of each area of the country, Whitman imagines himself literally becoming part of each one. In naming each place, he tries to call them into fellowship with himself- and with each other. As he personifies each river and sea, these natural features in turn make him more than human:

caribbean map "Mississippi with annual freshets and changing chutes, Missouri and Columbia and Ohio and Saint Lawrence with the falls and beautiful masculine Hudson, do not embouchure where they spend themselves more than they embouchure into him. The blue breadth over the inland sea of Virginia and Maryland and the sea off Massachusetts and Maine and over Manhattan bay and over Champlain and Erie and over Ontario and Huron and Michigan and Superior, and over the Texan and Mexican and Floridian and Cuban seas and over the seas off California and Oregon, is not tallied by the blue breadth of the waters below more than the breadth of above and below is tallied by him. When the long Atlantic coast stretches longer and the Pacific coast stretches longer he easily stretches with them north or south. He spans between them also from east to west and reflects what is between them."

Note that Whitman's view of "America" is not limited to the handful of states as of 1855. He imagines that many nearby territories- Cuba and Mexico- will eventually be part of this continental whole.

Identifying his own body with 'bodies of land' and 'bodies of water' in the Western Hemisphere, the poet becomes a kind of continent of his own. Trees grow out of him; birds flock to him:

 On him rise solid growths that offset the growths of pine and cedar and hemlock and liveoak and locust and chestnut and cypress and hickory and limetree and cottonwood and tuliptree and cactus and wildvine and tamarind and persimmon . . . . and tangles as tangled as any canebrake or swamp . . . . and forests coated with transparent ice and icicles hanging from the boughs and crackling in the wind . . . . and sides and peaks of mountains . . . . and pasturage sweet and free as savannah or upland or prairie . . . . with flights and songs and screams that answer those of the wildpigeon and highhold and orchard-oriole and coot and surf-duck and redshouldered-hawk and fish-hawk and white-ibis and indian-hen and cat-owl and water-pheasant and qua-bird and pied-sheldrake and blackbird and mockingbird and buzzard and condor and night-heron and eagle.

The metaphor of incarnation, finally, allows Whitman to claim a kind of political authority over the country as well. Because he knows the land so well- because he has become the land, in some sense- the American poet contains within himself "the essences of the real things and past and present events." More than mere politicians, he has his finger on the pulse of the nation, and is ready to express this reality in a way that is "transcendant and new."