The Iowa caucuses are not a primary. In fact they're not even an election.
The caucuses, which kick off the presidential nominating calendar, are official party meetings across the state's nearly 1,700 precincts. In high school gymnasiums, suburban libraries, and living rooms, Iowa voters express their candidate preference among their peers. Sometimes they'll submit their choices on pieces of paper. In other instances, they'll walk to corners of a room that represent their candidate.
The parties calculate their caucus winners in two different ways. It's simple for Republicans: They just tally supporters for each candidate across the state. Democrats require a threshold — usually 15 percent — of support for a candidate in each caucus. If a candidate doesn't reach 15 percent, their supporters are asked to pick another candidate, and the group will caucus again.
In both parties, the candidates with the most support get more delegates on caucus night. But for Democrats, the final tally is determined through a series of county and regional conventions in the months that follow caucus night.
Iowa map facts: 99 counties, 1,681 precincts
2. Emmet County
With a population of fewer than 10,000 people, this county is one of the state's most rural. There might be only a dozen people at some of the caucuses here, while there are hundreds who caucus at a single precinct in the state's larger cities.
3. Franklin County
For Republicans, one ballot is equal to one vote. Seems like simple math, right? Not in 2012. After party leadership declared Mitt Romney the winner on caucus night by eight votes, some precincts (including Geneva-Reeve in this county) reported some discrepancies. Weeks later, a full tabulation put Rick Santorum ahead of Romney by a few dozen votes.
4. Black Hawk County, Johnson County, and Story County
These areas include three of the state's largest universities. US Senator Bernie Sanders has support in these areas, but college students are usually first-time caucus-goers — and not always reliable.
5. Dubuque County
It's a blue-collar, Democratic-leaning, but socially conservative area of the state. This county provides a great test as to whether a candidate can win a swing state like Ohio.
6. Wayne County
In some of the less populous parts of the state like this, there are only a few precincts (four in this county). But there's no such thing as caucuses by absentee ballot: Caucus-goers have to be in the room. It's one of the reasons caucuses are usually dominated by diehard political activists. They always show up!
7. Dallas County
This suburban area west of Des Moines is a big battleground for Republicans. There are many evangelical voters — which make up more than half of all GOP caucus-goers — as well as more moderate business-minded Republicans.
8. Pottawattamie County
These mid-sized towns and cities along the Missouri River can help candidates rack up delegates. And because of the way Democrats do their delegate math, it's important for candidates to have a presence here — and almost every other precinct in the state. Hillary Clinton did well here in 2008.
9. Polk County
The county seat, Des Moines, is state's largest city and a Democratic stronghold. But because of the intricate way in which Democrats calculate their delegates, a large vote total in this area doesn't always equal a big victory. Democratic candidates must make sure their presence is spread out throughout the city to maximize their delegates, which are calculated proportionally by each precinct.