About OpenCMA
OpenCMA is an open-source comparative market analysis platform covering Ohio and California real estate. It aggregates data from public government APIs and free third-party services to produce comprehensive property reports covering valuation, tax history, demographics, environmental hazards, walkability, and market comparables — all at no cost to the user.
Coverage
Ohio — All 88 Counties
Six counties have dedicated scrapers pulling directly from county auditor ArcGIS servers: Cuyahoga (Cleveland), Franklin (Columbus), Hamilton (Cincinnati), Summit (Akron), Lucas (Toledo), and Wood (Bowling Green). The remaining 82 counties use the OGRIP statewide parcel database for basic parcel data. Ohio properties also receive state-specific enrichment including municipal income tax rates, Ohio EPA environmental layers, and Ohio DNR geological data.
California — 17 Counties
Dedicated county assessor scrapers for Alameda, Contra Costa, Humboldt, Los Angeles, Marin, Nevada, Orange, Riverside, Sacramento, San Diego, San Francisco, San Mateo, Santa Clara, Santa Cruz, Sonoma, Ventura, and the Tahoe area (Placer/El Dorado). California properties also receive state-specific hazard zone data, CalEnviroScreen environmental justice scores, and wildfire history.
Nationwide Enrichment
All properties — regardless of state or county tier — receive flood zone classifications, Census demographics, walkability scores, nearby amenities, earthquake history, wetland data, EPA-regulated facility data, and Superfund site proximity.
Data Sources
All data is fetched in real-time from public APIs. No property data is stored on our servers.
Nationwide & Global
U.S. Census Bureau Geocoder
Converts street addresses to geographic coordinates (latitude/longitude), Census tract codes, and county FIPS codes. Powers the address search.
Census American Community Survey (ACS)
Median household income, home values, owner/renter occupancy, vacancy rates, education levels, poverty rates, and population statistics at the Census tract level.
FEMA National Flood Hazard Layer
Flood zone classifications (A, AE, V, VE, X, D) with risk levels, base flood elevations, and flood zone boundaries from FEMA's public map service.
Walk Score API
Walk Score, Transit Score, and Bike Score ratings based on walking routes to nearby amenities, transit infrastructure, and biking conditions.
OpenStreetMap (Overpass API)
Points of interest within 1 mile: grocery stores, restaurants, parks, schools, hospitals, pharmacies, transit stops, banks, and fitness centers from crowd-sourced map data.
OpenRouteService
Drive-time isochrone polygons showing 5, 10, and 15-minute driving ranges from the property location. Visualized as map overlays.
USGS Earthquake Hazards Program
Recent and historical earthquake events within 100km of the property over the past 10 years, including magnitude, depth, and distance.
USFWS National Wetlands Inventory
Nearby wetland areas classified by type (freshwater, estuarine, riverine) from the U.S. Fish & Wildlife Service.
EPA ECHO (Enforcement & Compliance)
Facilities regulated under the Clean Air Act, Clean Water Act, RCRA, Safe Drinking Water Act, and Toxics Release Inventory within approximately 3 miles of the property.
EPA Superfund / NPL Sites
National Priorities List sites — the most serious known contaminated locations requiring long-term federal cleanup — within approximately 5 miles of the property.
Ohio
County Auditor ArcGIS Services
Parcel attributes, assessed/market values, building details, owner records, tax history, and sales data from county auditor GIS servers. Currently integrated for Cuyahoga, Franklin, Hamilton, Summit, Lucas, and Wood counties.
OGRIP Statewide Parcel Database
The Ohio Geographically Referenced Information Program maintains a statewide parcel dataset. Provides parcel boundaries, addresses, land use codes, and links to county auditor sites for all 88 Ohio counties.
Ohio Department of Taxation
Municipal income tax rates for Ohio cities and villages, plus school district income tax rates. Municipal rates from official publications; school district rates from the SD Rate Table with spatial boundary lookup.
Ohio EPA Environmental Sources
Brownfield sites, spill incidents, PFAS sampling locations, asbestos notifications, solid waste facilities, and water quality data near the property from Ohio EPA GIS layers.
Ohio DNR Geological & Water Resources
Karst geology features, oil and gas well locations, dam inventories, water well logs, and DRASTIC groundwater vulnerability index from the Ohio Department of Natural Resources.
County Sales Disclosures
Real estate transfer disclosure records from county auditor databases, providing recent sale prices and transaction details used for comparable sales analysis.
City Building Inspections
Property inspection records from municipal building departments, including permits, violations, and code compliance history.
California
California County Assessor GIS Services
Parcel attributes, assessed values, building details, and sales data from county assessor GIS servers. Currently integrated for Alameda, Contra Costa, Humboldt, Los Angeles, Marin, Nevada, Orange, Riverside, Sacramento, San Diego, San Francisco, San Mateo, Santa Clara, Santa Cruz, Sonoma, Ventura, and Tahoe-area (Placer/El Dorado) counties.
California Geological Survey (Hazard Zones)
Earthquake fault zones, liquefaction zones, landslide susceptibility, fire hazard severity zones, and tsunami evacuation areas from California state GIS services.
CalEnviroScreen
Pollution burden and population vulnerability scores by Census tract from the California Office of Environmental Health Hazard Assessment, identifying disadvantaged communities.
DTSC EnviroStor
Hazardous waste sites, cleanup activities, and land use restrictions tracked by the California Department of Toxic Substances Control.
CAL FIRE — Fire History
Historical wildfire perimeters and burn areas near the property from the California Department of Forestry and Fire Protection.
California Sales Tax Rates
Combined state and local sales tax rates by address from the California Department of Tax and Fee Administration.
CMA Methodology
The Comparative Market Analysis selects comparable properties from recent nearby sales, then applies dollar adjustments for differences in square footage, bedrooms, bathrooms, year built, garage capacity, lot size, and condition. Adjusted sale prices are weighted by similarity score to produce a value estimate range with confidence rating. Cross-validation is performed against assessed value ratios and area median price-per-square-foot.
Disclaimer
OpenCMA is provided for informational and educational purposes only. It is not a substitute for a professional appraisal, broker price opinion, or title search. Data is sourced from public APIs and may be incomplete, delayed, or inaccurate. Always verify information independently before making financial or legal decisions.