Every number on Bay State Atlas comes from somewhere. This page lists every source, when each was last refreshed, and any caveats. Currently tracking 194 Massachusetts towns.
What changed Aug 15, 2026
Refreshed every town's median home price against Zillow ZHVI June 2026. Roughly half the prices had drifted 5% or more since the initial launch. Every town now carries an as-of date and a source label directly under the price. Set up a monthly auto-sync so this never happens again.
Full audit table below. If a number still looks off, email me from the atlas and I'll fix it fast.
Zillow Home Value Index is a smoothed, seasonally adjusted measure of the typical home value in the middle third of the market (33rd to 67th percentile). Refreshed monthly. It's Zillow's own definition of a typical home in a place, so it's the number people will cross-check against when they look up your town on Zillow.
Caveat: ZHVI is deliberately tier-adjusted. For high-end towns like Brookline and Provincetown, ZHVI reads lower than the actual median sale price because the top and bottom deciles are trimmed. For those 2 towns we hold editorial median sale-price values instead. Every town card shows which source it uses.
Editorial median sale price
as of Q4 2025
Median home price for high-end markets where ZHVI understates.
Coverage
4 towns (Brookline, Provincetown, Boxborough, North Attleborough)
For towns where Zillow ZHVI reads meaningfully lower than closed-sale price data (luxury inventory or heavy vacation-home skew), we hold a manually researched median sale price sourced from MLS-derived aggregators. These are cross-checked against Redfin and Movoto at time of update. Refresh cadence is quarterly.
The 5-year ACS estimate is the Census Bureau's most reliable dataset for small towns. It's what every serious housing analyst uses. We refresh when the new vintage lands each December.
Caveat: ACS lags by 1 to 2 years. For places with recent shocks (a mill closing, a new corporate campus) the number is directionally right but not real-time.
Peak commute minutes to South Station modeled from CTPS regional travel-demand data, cross-checked against Google Maps typical-traffic times sampled across a Tuesday morning window. Values represent typical, not worst-case.
0-100 composite blending MCAS performance, accountability percentile, and per-pupil spending, calibrated to Niche's public methodology so ratings are comparable to what buyers see elsewhere.
We take the max of FEMA's inland (IFLD) and coastal (CFLD) national-percentile risk scores per Census tract, then population-weight across the tracts that overlap each town. Higher score = SAFER (less risk). Categorical labels come straight from FEMA.
Caveat: SFHA-based flood metrics miss most stormwater flooding. MAPC 2023 found 96% of recent claims were outside SFHAs. Treat as a floor, not a ceiling.
Freddie Mac PMMS mortgage rates
as of week ending 2026-09-03
30-year and 15-year fixed rate averages powering the monthly payment estimates on every town card.
The Primary Mortgage Market Survey has been the industry-standard weekly rate benchmark since 1971. Freddie Mac collects loan-application data from lenders across the country and publishes the average 30-year and 15-year fixed rates every Thursday at noon ET. Bay State Atlas caches the latest reading and refreshes it weekly. Current 30-year fixed: 6.71%.
Caveat: Payment estimates on town cards assume 20% down, 30-year fixed, principal and interest only. Real payments include property taxes, insurance, and possibly PMI, which vary meaningfully town-to-town.
Every archetype tag ('Trail Town', 'Coastal Quiet', 'Family Hub'), every hidden-gem flag, and the one-line tradeoff on every town are editorial calls by Gary Fikes, MA Real Estate Agent #9560266 at MP Signature Realty. These are opinions, not data. They're clearly separated from the numeric fields.
The freshness promise
Prices auto-sync every month against Zillow ZHVI. If any town drifts more than 3%, I get an email and the site gets updated within 24 hours.
Everything else (income, commute, schools, flood risk) gets a manual pass when new source data lands. Those refresh windows are listed above.