Methodology, disclaimers & data corrections

Parcel Context is an evidence-first public-records research platform covering Sacramento, San Francisco, Marin, Yolo, Alameda, and Contra Costa counties. Every figure displayed on the site carries its upstream source, geography, and reporting or retrieval period.

1. How we handle public records & provenance

Snapshot-dated change history: Many municipal permit portals overwrite a record's current status without publishing a timestamp for the change. Rather than inventing a status date, our ingestion pipeline archives snapshots of each upstream feed and dates discovered status changes to the window between consecutive snapshots ([observed_prev_at, observed_at]).

Project grouping is an explicit inference: A single development often spans multiple building permits, demolition permits, and California HCD Housing Element Annual Progress Report (APR) entries. Our entity resolver groups related records by Assessor's Parcel Number (APN), normalized street address, and cross-referenced record numbers, and displays the exact rule used for each link on the project page.

Neighborhood census statistics & margins of error: Census American Community Survey (ACS) 5-year estimates are published for census block groups and tracts, which do not align with city neighborhood boundaries. We apportion partial block groups using 2020 Decennial Census block housing-unit counts and compute 90% margins of error from the Census Bureau's 80 variance replicate tables. Estimates with a high coefficient of variation are flagged with caution or marked unreliable.

Preserving distinctions: We never blend area-level rent benchmarks (HUD Fair Market Rents, Census ACS medians) or area home-value indices (Zillow ZHVI) into a single property-specific valuation or rent estimate.

2. Disclaimers & non-reliance notice

No appraisal or valuation: Parcel Context does not appraise real estate or predict future property values or rents. Area benchmarks (Census ACS, HUD FMR, Zillow ZHVI) describe surrounding ZIP codes or neighborhoods, not individual parcels.
No legal, tax, zoning, or financial advice: The “What could be built here” screen (ADU / SB 9), the Proposition 13 property-tax estimator, and the rental regulatory context (AB 1482 and local rent ordinances) are informational screens built from public maps and statutes. Local ordinances, recorded easements, CC&Rs, historic resources, tenancy history, and site conditions can change eligibility. Always verify with the local planning department, county tax collector, or qualified counsel before making financial or development decisions.
Hazard overlays are map citations, not safety scores: FEMA National Flood Hazard Layer (NFHL) zones, CAL FIRE Fire Hazard Severity Zones (FHSZ), and California Geological Survey (CGS) Alquist-Priolo Earthquake Fault Zones are shown as published by each agency with links to the official maps.
Parcel boundaries: GIS parcel polygons come from county assessor maps, are published for assessment purposes only, and do not constitute a legal land survey.

3. Data sources & required attributions

View live source freshness ledger →

Municipal & County GIS / Permit Feeds: City of Sacramento Open Data (Building Permits, Zoning, 2040 General Plan, Neighborhoods); Sacramento County GIS Open Data (Parcels, Address Points); City and County of San Francisco (DataSF / Department of Building Inspection / Planning); County of Marin Community Development Agency (ODbL); Yolo County GIS & City of West Sacramento; Alameda County GIS & Cities of Oakland, Fremont, and Hayward; Contra Costa County GIS & City of Richmond.

State & Federal Datasets: California Department of Housing and Community Development (HCD Housing Element Annual Progress Reports); CAL FIRE Office of the State Fire Marshal (Fire Hazard Severity Zones); California Geological Survey (Alquist-Priolo Earthquake Fault Zones); Federal Emergency Management Agency (FEMA National Flood Hazard Layer); U.S. Census Bureau (2020 Decennial Census Blocks, TIGER/Line ZCTAs, and 2020–2024 American Community Survey 5-Year Variance Replicate Estimates); U.S. Department of Housing and Urban Development (Fair Market Rents and Small Area Fair Market Rents).

Zillow Research Data: Home-value index series are sourced from Zillow Research (Zillow Home Value Index, ZHVI). Data provided by Zillow. Used under Zillow's non-commercial public research terms with attribution.

4. Requesting a data correction or record review

Because Parcel Context reproduces public records as published by city, county, state, and federal agencies, most underlying address, parcel-boundary, zoning, or permit-status errors originate in the upstream agency dataset. Every property dossier includes an Official records section linking directly to the agency's authoritative portal so you can compare our snapshot with the live agency record.

If you find an error in our project grouping, taxonomy classification, census area apportionment, or a stale record that has been corrected upstream, please include:

The full URL of the Parcel Context property (`/properties/[apn]`) or project (`/projects/[id]`) page.
The specific permit number, HCD tracking ID, or statistic in question.
A link to or screenshot of the corrected official agency record.

Privacy & PII policy: Parcel Context does not publish property owner names, telephone numbers, or personal email addresses. Any operator identifiers in upstream feeds are cryptographically hashed during ingestion.