The Washington Post has a great interactive map on the Political Geography of the Iowa Caucus. Each candidate is studying the geography of Iowa in order to try to win the state.
Mike Huckabee: Huckabee is focusing on the rural, conservative northwestern section of the state. Christian conservatives are more concentrated here (anyone who knows that region knows it is filled with 'Dutch').
Mitt Romney: Romney is going where the votes: Des Moines and Cedar Rapids. He has been in the state for along time and hopes his ground network can suppress the Huckabee insurgency.
Barak Obama: Obama's campaign of "hope and energy" is focusing on youth. In particular Obama is focusing on the university towns of Ames (Iowa State University), Cedar Falls (University of Northern Iowa), and Iowa City (University of Iowa). This may be a smart strategy because the students at these universities will be on break and spread all throughout the state. Obama may have his own missionaries engage in fifth generation warfare (5GW).
John Edwards: Edwards is a union man and has centered his energy around Des Moines and the industrial and populist farmer town of Newton. His energy here has cost him somewhat with possible support from other blue-collar areas like the Mississippi River Coast and Sioux City.
Hillary Clinton: Clinton is focusing on the middle class, (sub)urban woman. The natural environment in Iowa for these women is Des Moines. Attention here has cost here with other caucus voters elsewhere in the state.