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NYC's 2021 Ranked Choice Vote Mapped in Detail

Posted August 24, 2021


New York's first citywide election using ranked choice voting has now been mapped in detail by the Center for Urban Research (CUR) at The Graduate Center of the City University of New York (CUNY).

The NYC Ranked Choice Voting Map shows the local patterns of the city's ranked choice vote (RCV) tallies for the June 2021 primary. The map is the first-of-its-kind that visualizes multi-candidate vote patterns at the local level. It will help members of the public, journalists, elected officials, and others to understand the hyperlocal patterns of June 2021 Democratic primary results for Mayor and Comptroller.

John Mollenkopf, Center for Urban Research director and distinguished professor of Political Science and Sociology at the Graduate Center, noted that we now have the most detailed look at one of the most momentous elections in New York City history. This will allow us to explore all the ins and outs of an election that promises to change the tenor of city politics for years to come.

Special thanks to the following (see Credit section below for more details):

Using the map

For each election district and Assembly district, CUR's map provides a powerful visual display of the vote flow during the RCV tallies for each candidate using a color-coded Sankey diagram (see example):

  • The diagram shows the number of votes allocated by district from each round's eliminated candidates to the remaining candidates.
  • Text below the diagram displays the exact number of votes.
  • The Sankey diagram is updated instantly as you hover over or click on any of the 5,600 election districts or 65 State Assembly districts on the map.
  • Clicking on a district on the map selects that district so you can view its specific RCV vote tallies. Click that district again to unselect it so you can view the info for other districts.

The Sankey diagram also highlights where votes were rendered inactive in each RCV round. This reveals if inactive votes are concentrated by neighborhood, and locally how much of each eliminated candidate's votes were rendered inactive.

The online map itself shows round-by-round vote share by district for each candidate. An RCV Rounds slider feature enables you to change the map display from one round to the next to see how each candidate's vote share increased as votes were allocated from eliminated candidates.

In the NYC mayoral primary, 3 candidates were eliminated in Round 6 using "batch elimination" (their combined votes were less than the candidate with the next-highest number of votes). In order to calculate how the votes from each of these 3 eliminated candidates were allocated individually, CUR separated the vote tallies for Round 6 into three separate "rounds": 6a, 6b, and 6c. The RCV Rounds slider reflects this approach. Calculating the candidate votes in this way does not affect the final vote outcome, but makes the mapped patterns more precise.

More maps and analysis of the RCV vote patterns are available via the CUNY Graduate Center's NYC Election Atlas: citywide vote flow diagrams and detailed maps.

The RCV map

See the full map at

Inital takeaways

The visualizations on the map reveal numerous interesting patterns. Here are just some of the relationships you'll see when you explore the map (the links below open a new window highlighting each area noted below, as an example illustrating each point):

  • Toward the end of the mayoral campaign, Andrew Yang joined with Kathryn Garcia and urged his supporters to rank Garcia second on their ballots. In some areas this seems to have succeeded. But in other areas, Yang's voters decided otherwise. In Assembly district 48, for example, covering the Borough Park and Midwood neighborhoods of Brooklyn, almost all of Yang's votes were allocated to Eric Adams and almost none to Garcia.
  • Many observers expected Maya Wiley and Kathryn Garcia's voters to pick these candidates first and/or second. In almost all Assembly districts where Wiley did best, that expectation held true: most of her ballots were transferred to Garcia. But in areas where Eric Adams did well, Wiley's votes were often transferred to Adams rather than to Garcia.
  • Despite Yang's support for ranked choice voting, many voters in certain neighborhoods appear to have either ranked only Yang, or Yang and none of the other frontrunners. For example, most of Yang's ballots in Assembly district 49 in south Brooklyn and Assembly district 40 in northeast Queens were rendered inactive (i.e., "exhausted") after Yang was eliminated in Round 7. His remaining votes were split between Adams and Garcia in those ADs.

Later in fall 2021, CUR will analyze the RCV vote results in relation to local demographic data and other vote patterns. The Center is partnering with Common Cause New York on this research project.

Data sources

The RCV vote tallies are obtained by aggregating data by district from the New York City Board of Elections. The Board of Elections published the cast vote record (CVR) for the June primary, detailing the ranking for each ballot certified by the Board. The cast vote record data is anonymous. CUR used special software to convert the individual ballot records to aggregate vote counts by district.

N.B.: although the Board of Elections provided easy access to the CVR files online, the file formats were inconsistent, and the Board provided no documentation for the data. CUR parsed the data to the best of our ability, but vote tallies on the map may not exactly match vote totals certified by the Board. Absent any guidance from the NYC Board of Elections, the map reflects as accurate a picture of the RCV vote patterns as possible.

Boundaries for election districts and New York State Assembly districts are provided by the New York City Department of City Planning's Bytes of the Big Apple project.


The RCV map was developed by the Center for Urban Research at The Graduate Center, CUNY, led by John Mollenkopf, through CUR's Mapping Service coordinated by Steven Romalewski. The Mapping Service's senior application architect Will Field designed, created, & coded the application. Valerie Bauer, a graduate of Lehman College's Geographic Information Science program, customized the d3 Sankey diagram code for this application, compiled and analyzed the data behind the map, and helped develop the map designs & color themes.

Funding support for CUR's analysis of New York's ranked choice vote patterns comes from the Common Cause NY Education Fund.

Our ability to analyze NYC's ranked choice vote data by election district is due to the availability of the open source RCV Tabulator software, developed by the Ranked Choice Voting Resource Center. The leading organization supporting RCV reforms nationwide - FairVote - also provided helpful advice and guidance. FairVote has also prepared its own analysis of the city's cast vote record data.

The application itself is built using a mix of web development tools and technologies including:

  • Mapbox, which is providing generous support hosting the RCV map layers, as well as static tiles for features such as place names, points of interest, and waterbodies;
  • several JavaScript libraries including Vue (enhanced with Vuetify), d3, and Node; and
  • all the data for the map is managed via Postgres and PostGIS, hosted by the Graduate Center.