U.S. county home values — 10 years + 12-month forecast

Each arrow is a U.S. county. Angle and color encode the 12-month percent change in Zillow’s ZHVI; longer arrows mean larger changes. The slider covers 120 historical months (Apr 2016 → Mar 2026) followed by a 12-month forecast; forecast frames render at lower opacity. The fan chart below the map shows the national outlook with 50 / 80 / 95% prediction intervals.

— Percent change (12-month)

How to read this map

Each arrow sits at the centroid of one U.S. county. Its angle reports the sign of the year-over-year change in the Zillow Home Value Index — sharply upward for a big increase, downward for a decline, near horizontal when prices are flat. Color redundantly encodes the same value, and length grows with magnitude.

The slider walks through 120 historical months and 12 forecast months. Forecast frames render at lower opacity; the timeline track switches to dashed grey at the boundary. The fan chart below the map shows the national outlook.

Forecast model

Per-county point forecasts come from Holt's exponential smoothing with damped trend (statsmodels). The smoothing-trend coefficient is bounded to (0, 0.05) and the damping coefficient to (0.5, 0.85) — without those bounds the optimiser reads a recent monthly dip as a permanent slope and projects unrealistic moves twelve months out. With the bounds the forecast asymptotes near the smoothed level.

The fan chart's bands come from 500 stochastic simulations of the fitted national model (mean YoY across counties), with quantiles at 2.5/10/25/50/75/90/97.5%. They are model intervals — they capture residual variance, not regime change or major policy shifts.

Reference

Inspired by a piece in The Wall Street Journal that mapped county-level home-insurance change with the same angled-arrow idiom.

Data & method

Home values come from Zillow’s ZHVI (county, all homes, smoothed, seasonally adjusted). For each month we compute the 12-month percent change against the same month one year earlier. Values are clipped to ±20% for the visual encoding only; tooltips show the unclipped figure.

Boundaries are U.S. Census TIGER 2022 simplified counties via the us-atlas project, projected with d3.geoAlbersUsa, which places Alaska and Hawaii in the conventional inset positions. Counties without a Zillow series for the period are not drawn.