How GroundTally works

Every business day we ingest issued building permits from 12 metro open-data portals (Socrata and ArcGIS APIs), archive the raw records verbatim, and normalize each permit into one event model: timestamp, location, permit class, trade, valuation, and contractor.

Normalization that matters

• Project-level valuations. Cities issue multiple section permits that each repeat a project's full value — naive totals overstate construction by up to 21x. We deduplicate to projects before summing anything.
• Renewals excluded. New York permit renewals are filtered out of activity counts.
• One taxonomy. Twelve different permit vocabularies map to one residential/commercial and trade classification, with per-city coverage documented below.

Validation against official statistics

Monthly, we compare our new-residential-construction counts against the U.S. Census Bureau's Building Permits Survey — the official statistic, published with a ~2-month lag. GroundTally's value is the same signal, weeks earlier and at permit-level detail. The current comparison:

GroundTally vs Census Building Permits Survey

BPS counts new residential buildings authorized per month (official statistics,

~2-month lag, city-jurisdiction scope). GroundTally column = permits matching each

source's new-residential-construction vocabulary. Levels differ where jurisdiction

boundaries differ; the trend correlation (Pearson r on monthly counts) is the

validation signal.

Austin — r = 0.91 (tracks official data), level ratio 1.41x

Baton Rouge — r = 0.37 (weak correlation), level ratio 0.40x

Chicago — r = 0.53 (weak correlation), level ratio 2.46x

Cincinnati — r = 0.83 (tracks official data), level ratio 0.56x

Los Angeles — r = 0.87 (tracks official data), level ratio 1.17x

Montgomery County — r = 0.33 (weak correlation), level ratio 3.41x

New York — not comparable yet

New-building classification requires joining a separate source dataset.

Norfolk — r = 0.87 (tracks official data), level ratio 2.01x

Raleigh — r = 0.82 (tracks official data), level ratio 0.82x

San Francisco — r = 0.75 (tracks official data), level ratio 1.38x

Seattle — r = 0.98 (tracks official data), level ratio 1.10x

Washington — r = 0.57 (weak correlation), level ratio 1.37x

Summary

• Austin: r=0.91 (tracks official data)
• Baton Rouge: r=0.37 (weak correlation)
• Chicago: r=0.53 (weak correlation)
• Cincinnati: r=0.83 (tracks official data)
• Los Angeles: r=0.87 (tracks official data)
• Montgomery County: r=0.33 (weak correlation)
• New York: n/a
• Norfolk: r=0.87 (tracks official data)
• Raleigh: r=0.82 (tracks official data)
• San Francisco: r=0.75 (tracks official data)
• Seattle: r=0.98 (tracks official data)
• Washington: r=0.57 (weak correlation)

Known scope caveats

• Chicago / Washington DC: no residential flag in the source; our count includes commercial new construction.
• Baton Rouge: ours covers all of East Baton Rouge Parish; BPS row = city + unincorporated parish only.
• Montgomery County: BPS row is the unincorporated area; incorporated cities (Rockville, Gaithersburg) file separately.
• BPS current-month files are preliminary and revised later; we re-fetch on every run.