New York City is using ranked choice voting in its Democratic mayoral primary election. Here's how it works: Rather than pick just one candidate, voters get to rank several in order of preference.

The race to pick the Democratic nominee for mayor ends Tuesday with primary Election Day — and so far early voting has surged to nearly twice the turnout of four years ago.

Voters in the Democratic mayoral primaries are able to rank their top five candidates, but are not required to fill all five slots. If a candidate gets over 50% first-choice votes, they win. But if not, the candidate with the fewest votes is eliminated as votes are counted in subsequent rounds.