openapi: 3.0.3
info:
  title: HUD User CHAS ZIP Code Crosswalk API
  description: Comprehensive Housing Affordability Strategy (CHAS) data provides custom tabulations of American Community Survey (ACS) data on housing needs at national, state, county, place, and census tract levels. CHAS data is used for Consolidated Planning submissions required to receive HUD formula grant funds. Requires a free bearer token obtained from the HUD User portal.
  version: 1.0.0
  contact:
    name: HUD User Support
    url: https://www.huduser.gov/portal/contact.html
  license:
    name: Public Domain
    url: https://www.huduser.gov/portal/dataset/api-terms-of-service.html
servers:
- url: https://www.huduser.gov/hudapi/public
  description: HUD User Public API
security:
- bearerAuth: []
tags:
- name: ZIP Code Crosswalk
  description: ZIP code to geographic area crosswalk queries
paths:
  /usps:
    get:
      summary: ZIP Code Crosswalk Query
      description: Returns crosswalk data mapping ZIP codes to and from other geographic units. Supports multiple crosswalk types including ZIP-to-county, ZIP-to-census tract, ZIP-to-CBSA, ZIP-to-congressional district, and ZIP-to-county subdivision.
      operationId: getZIPCrosswalk
      tags:
      - ZIP Code Crosswalk
      parameters:
      - name: type
        in: query
        required: true
        description: 'Crosswalk type code: 1 = ZIP to County, 2 = ZIP to Census Tract, 3 = ZIP to CBSA, 4 = ZIP to Congressional District, 5 = County to ZIP, 6 = Census Tract to ZIP, 7 = CBSA to ZIP, 8 = Congressional District to ZIP, 9 = ZIP to County Subdivision, 10 = County Subdivision to ZIP'
        schema:
          type: integer
          minimum: 1
          maximum: 10
          example: 1
      - name: query
        in: query
        required: true
        description: The geographic identifier to look up. For ZIP-to-X queries, provide the 5-digit ZIP code. For X-to-ZIP queries, provide the appropriate geographic code (e.g., 5-digit FIPS for county, 11-digit FIPS for census tract, CBSA code, etc.)
        schema:
          type: string
          example: '20001'
      - name: year
        in: query
        required: false
        description: Year for crosswalk data (2nd quarter data)
        schema:
          type: integer
          example: 2023
      - name: quarter
        in: query
        required: false
        description: Quarter for crosswalk data (1-4)
        schema:
          type: integer
          minimum: 1
          maximum: 4
          example: 4
      responses:
        '200':
          description: Successful response with crosswalk data
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/CrosswalkResponse'
        '401':
          description: Unauthorized - missing or invalid bearer token
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '400':
          description: Bad request - invalid parameters
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
        '404':
          description: No crosswalk data found for the given query
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
components:
  schemas:
    ErrorResponse:
      type: object
      properties:
        message:
          type: string
          description: Error message
          example: Unauthorized access. Please provide a valid bearer token.
    CrosswalkRecord:
      type: object
      description: A single crosswalk mapping record
      properties:
        zip:
          type: string
          description: 5-digit USPS ZIP code
          example: '20001'
        county:
          type: string
          description: 5-digit county FIPS code
          example: '11001'
        geoid:
          type: string
          description: Geographic identifier for the target geography
          example: '11001'
        tract:
          type: string
          description: Census tract code (11-digit FIPS)
          example: '11001000100'
        cbsa:
          type: string
          description: CBSA (Core Based Statistical Area) code
          example: '47900'
        cd:
          type: string
          description: Congressional district code
          example: '1100098'
        res_ratio:
          type: number
          description: Ratio of residential addresses in the ZIP that map to this geography
          example: 0.85
        bus_ratio:
          type: number
          description: Ratio of business addresses in the ZIP that map to this geography
          example: 0.9
        oth_ratio:
          type: number
          description: Ratio of other addresses in the ZIP that map to this geography
          example: 0.8
        tot_ratio:
          type: number
          description: Ratio of total addresses in the ZIP that map to this geography
          example: 0.86
    CrosswalkResponse:
      type: object
      properties:
        data:
          type: object
          properties:
            results:
              type: array
              items:
                $ref: '#/components/schemas/CrosswalkRecord'
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: Bearer token obtained by registering at https://www.huduser.gov/hudapi/public/register
externalDocs:
  description: HUD User CHAS API Documentation
  url: https://www.huduser.gov/portal/dataset/chas-api.html