{"id":568,"slug":"zillow-built-on-administrative-data-backbone","title":"Zillow: 110M-home \"living database\" built on Census/ACS + 3,000 county assessors + USPS + MLS feeds","kind":"reference","scope":"business","status":"current","audiences":["claude-code","candid-team"],"topics":["open-data","data-infrastructure"],"reference_body":"**Claim:** Zillow's database is *\"built on a backbone of administrative data\"* — Census, ACS, ~3,000 county tax assessments, sales records. The Zestimate model sits **on top of** public records, not beside them.\n\n**Sources:**\n- <https://apps.bea.gov/fesac/meetings/2016-06-10/Rao-Presentation-The-Zillow-Experience.pdf>\n- <https://www.zillow.com/tech/public-data-challenges/>\n\n**Confidence:** Verified.\n\n**Practitioner reference (from Zillow's own engineering blog):**\n- **Address Validation Service** runs assessor records against a GIS table of ~500,000 city/state/zip/county permutations to catch upstream errors before they reach the front end\n- **FillRate** per field per county tracks data completeness\n- **Transaction Latency** = Median (Transaction Recorded Date − Transaction Received Date) — the cleanest \"speed-of-data\" metric in public real-estate engineering\n\n**The pattern:** Zillow is fundamentally an open-data company. The MLS feed is value-added; the public-records cleaning is the moat. **Note:** Zillow's ZTRAX dataset was discontinued in 2023, but the technical writing remains the best public account of how a major operator handles public-records cleaning.","rationale_body":null,"metadata":null,"links":{"outgoing":[],"incoming":[{"slug":"attom-500m-transactions-2690-counties","title":"ATTOM Data: 500M+ real estate/loan transactions, 2,690+ counties, 20-step Enterprise Data Management Program","kind":"reference","scope":"business","link_type":"relates-to"},{"slug":"carfax-1984-10000-records-fax-to-35-billion","title":"Carfax: from 10,000 records faxed in 1986 to 35B+ records across 151,000+ sources — sold to S&P Global Mobility 2022","kind":"reference","scope":"business","link_type":"relates-to"},{"slug":"research-brief-public-data-private-moat","title":"Research brief: Public data as a private moat — building proprietary intelligence from government open data (piece 11 of 15)","kind":"reference","scope":"business","link_type":"relates-to"}]},"created_at":"2026-05-22T20:32:45.207Z","updated_at":"2026-05-22T20:32:45.207Z"}