Boundary Atlas

How to match members or supporters to their legislative districts

Place each member's address in its congressional, state senate and state house districts, then count members per district. The 2026 maps include the mid-decade redraws, so a list matched before 2025 may be out of date.

Who this is for

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With Boundary Atlas added to Claude, ChatGPT, Cursor or Codex (free, no key; how):

Match each member's address to their congressional and state legislative districts with Boundary Atlas and give me member counts per district.

Step by step

  1. Geocode. Census batch geocoder, up to 10,000 addresses a file.
  2. Locate. locate_point for each point; keep the district IDs.
  3. Count. Group by district ID. related_geographies on a district lists its counties and cities for context.
  4. Add officials. Boundary Atlas has districts, not legislators. Join district IDs to a legislator dataset for names.

Live example

233 S Wacker Dr, Chicago (Willis Tower), at 41.8786, -87.6362:

LevelResult
City or townChicago
CountyCook County
ZIP code60606
Congressional districtIllinois's 7th congressional district (IL-07)
State senate districtState Senate District 5
State house districtState House District 9
Voting precinct42014
StateIllinois
MayorBrandon Johnson
U.S. RepresentativeDanny K. Davis (D)
U.S. SenatorRichard J. Durbin (D)
U.S. SenatorTammy Duckworth (D)
State SenatorLakesia Collins (Democratic)
State RepresentativeYolonda Morris (Democratic)
City websitechi.gov
City councilChicago City Council
County websitewww.cookcountyil.gov
locate_point(lat=41.8786, lon=-87.6362)

Things to know

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