Methodology

Groundwork's job is to show what's actually happening. That means being clear about where each number comes from and what it can and can't tell you. Every number on the site links back to its source, and every chart says when its data was last updated.

How the data is organized

Everything charted on Groundwork is an observation: one value, for one place, for one period, from one named source. Each observation records the jurisdiction, the metric (say, typical asking rent), the period it covers, the value, the source, and the date the data was current. Panels are just different windows onto that one table. That's why every chart can offer the same data as a plain HTML table, and why every figure is traceable.

Rents (Zillow ZORI)

Rent figures come from the Zillow Observed Rent Index (ZORI). It measures asking rents, meaning what landlords list vacant units for, not what sitting tenants currently pay. That makes it move earlier and more sharply than average-rent measures. Zillow builds it as a repeat-rent index: it compares the same unit across successive listings and smooths the result, which damps one-off swings from whatever mix of units happens to hit the market in a given month. The tradeoff is coverage. The index needs enough listings to be reliable, so the smallest towns fall out. In our area, Belvedere, Clayton, Fairfax, and Ross have no rent series at all. They're absent from the rents chart, not at zero.

Home values (Zillow ZHVI)

Home value figures come from the Zillow Home Value Index (ZHVI). Where ZORI is about asking prices for rentals, ZHVI estimates the value of the housing stock itself: what a typical home in a place is worth, not just the handful that sold last month. Zillow models a value for essentially every home from sales, tax records, and listing data, then averages across the middle of the market and seasonally adjusts. That makes it steadier and more representative than median sale prices, which jump around with whatever mix of homes happened to sell.

Building pipeline (HCD Annual Progress Reports)

Permit and completion counts come from the Annual Progress Reports every California jurisdiction files with the Department of Housing and Community Development (HCD). The raw material is Table A2, a project-by-project list of housing activity. We aggregate those rows into one figure per jurisdiction per year. Income categories follow the RHNA rollup: acutely-low and extremely-low income units fold into very-low, and deed-restricted and non-deed-restricted units at each level are summed. Keep the big caveat in mind. These numbers are self-reported by jurisdictions, and HCD does not independently verify them.

One more wrinkle: the most recent year is provisional. Reports were due in April, late filers keep arriving, and the latest year's counts typically rise for months after first publication. Treat the newest bar as a floor, not a final figure.

We soften that problem two ways. The pipeline chart says how many of the 48 jurisdictions have reported the latest year so far. And when a jurisdiction hasn't reported at all, we fill in its prior-year figure as a placeholder rather than letting a missing report masquerade as zero construction. The placeholder is drawn lighter on the chart and marked "(est.)" in the table. Reported figures can still be amended upward. Once we've archived enough monthly snapshots of the dataset, we plan to replace the prior-year placeholder with an empirical completion estimate, and we'll explain that method here when it ships.

We also cross-check APR permit counts against the Census Building Permits Survey every refresh. The two use different definitions. The Census survey counts new privately-owned buildings and misses most ADUs and conversions, so APR normally runs higher, dramatically so in small cities where ADUs dominate. Our check flags the cases that genuinely deserve scrutiny: years where the Census count exceeds a city's APR count, which shouldn't happen if the APR is complete, and extreme gaps at high volume. A human reviews every flag. Flags never silently change a number on this site.

When a jurisdiction is absent from the data for a year, that means it reported no activity, not that the data is missing. We show a trailing five-year window, refresh the data roughly monthly, and stamp every chart with a “data as of” date so you always know how current the numbers are.

RHNA pace

Every California jurisdiction gets an eight-year housing target, its Regional Housing Needs Allocation (RHNA), split across four income bands. The Bay Area's 6th cycle runs from January 31, 2023 to January 31, 2031. A raw progress percentage flatters everyone early in the cycle, so we show prorated pace instead: how far along a jurisdiction should be by now if it were building steadily. If a city is 44% of the way through the cycle, being on pace means having permitted 44% of its target. We divide what it has actually permitted by that prorated target, so 100% is exactly on pace and 16% means it's permitting at about a sixth of the rate its own target requires.

Allocations and cumulative permits both come from HCD's RHNA Progress Report, which HCD compiles from the same self-reported annual reports and which therefore lags. We prorate the target to that data's own reporting date so the two sides of the ratio are measured at the same moment. HCD publishes only the raw cumulative share; the prorated pace is ours, and it's the number worth arguing about, so the underlying counts are right there in the table.

How recommendations are scored

The recommendations page scores each option 1–5 on four dimensions: supply impact (how much housing it could unlock), evidence strength (how solid the research behind it is), public cost (higher is cheaper, so a 5 is near-free to the public purse), and speed (how soon it could matter). Higher always means more attractive. The ranks are our judgment given the scores and the named tradeoffs, not a formula. Every score is contestable, and each entry links its sources so you can argue with us.

Legal tracker

The legal developments page is curated by hand from primary sources: statute text, ordinances, agency guidance, and court filings. Every entry carries the date we last reviewed it. Each one separates what the law says as written from what's actually happening on the ground, because in housing law the gap between the two is usually the story. The one part we don't maintain by hand is the compliance strip at the top. That loads from HCD's housing element compliance dataset, which refreshes weekly.

The full list of datasets, licensing, and links is on the sources page. Every number on the site links back to one of them.