Data sources
Data sources
Section titled “Data sources”What’s live, how often it refreshes, which vintage you’re looking at, and where it doesn’t reach. Attribution and upstream terms: attributions. Vintages below are as-of 2026-07-09; /api/tracts/chicago carries the exact vintage block for the data it’s actually serving.
Current feeds
Section titled “Current feeds”| Source | Used for | Cadence | Vintage | Coverage |
|---|---|---|---|---|
| Cook County Assessor (Socrata) | live comp sales + characteristics | per request | rolling 6-yr window | Cook |
| Cook Assessor reassessments | tax-shock by township | each triennial mailing | latest triad; South triad reassessing 2026 | Cook |
| Cook Clerk tax rates | effective property tax | annual | 2023 rates | Cook munis only |
| Chicago Data Portal | permits (18 mo), licenses (12 mo), 311 water-in-basement (3 yr) + governance (12 mo), crime (TTM vs prior), violations/vacancy | monthly | rolling windows | Chicago only |
| CFPB HMDA | capital flow, borrower income, FHA share | annual | flow 2022→2024; income 2024; FHA 2023 | Cook + Lake |
| Census LODES | workplace job growth | annual, lagged | 2019→2022 | Cook + Lake |
| Census ACS | pre-1980 housing stock (B25034) | annual | latest 5-yr | Cook + Lake |
| HUD SAFMR | rent anchor, voucher ceilings, S8 arbitrage | annual | FY2026 | by ZIP |
| Zillow ZHVI/ZORI | prices, rents, gross yield | monthly | latest month | ZIP; ZORI ~288 IL ZIPs |
| Redfin (listings) | primary listings feed | daily 13:00 UTC + monthly sweep | same-day | Cook + Lake on-market |
| Redfin Data Center | sale-to-list, DOM, market heat | quarterly | latest quarter | ZIP |
| CTA ridership | L-station recovery vs 2019 | monthly | ≥ 2025-04 vs 2019 baseline | ~0.75 mi of stations |
| FEMA NFHL | flood-zone flag | static | current NFHL | Cook + Lake |
| Lake County GIS | parcels (57k 1970–88 SFHs), flood, schools | static export | as exported | Lake |
| OSM / OSRM | amenity clusters, commute times | with refresh | OSM-dependent | variable |
Known gaps
Section titled “Known gaps”| Gap | Consequence |
|---|---|
| Lake County tax rates unavailable (portal down) | Lake tracts carry no tax signal; the BRRRR low-tax weight is silent there |
| Chicago-only feeds: permits, licenses, 311, crime, distress, ridership | suburban tracts miss those signals entirely and lean on the county-wide feeds |
| ZORI covers ~288 IL ZIPs, ZIP-blended | a hot block inherits its ZIP median; thin-ZORI areas fall back to SAFMR |
listed_at falls back to first-seen |
true days-on-market arrives with MLS data (P7) |
| Redfin scraping is a bridge, not a foundation | licensed property-data API is decision gate G2 (P5) |
Planned, in wiring priority order
Section titled “Planned, in wiring priority order”DePaul IHS 2–4 unit indicators (quarterly), CCAO open assessment model + sales flat files, Board of Review appeals by PIN, FHFA tract-level HPI, Lake County recorder (now free), OpenFEMA NFIP claims + National Risk Index, Eviction Lab/LCBH, CCLBA/ChiBlockBuilder inventory, Fannie/Freddie REO feeds, EPA FRS/LUST, LiDAR/soils/imagery, Census Building Permits Survey (the honest suburban-permits patch), FRED/BLS cost indices. Paid picks under the standing $50/mo data budget (prices verified 2026-07-08): RentCast free tier, Google Street View Static, Rentometer Pro — ~$25–42/mo total. Every adopted feed gets a data contract — schema, cadence, freshness SLO, null-rate SLO, vintage tag — before its signal ships to the map.