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How a call is counted
Either a county's own dispatcher put a neighbor's unit on its box —
"Box 41-20, Engine 401, Carroll County Medic 139, chest pains" — or a dispatch
declared an outbound run, "mutual aid into Harford County". Anchoring the county
name to an apparatus noun is what keeps Harford Road, a Baltimore City street, out
of the Harford County totals.
Why "help given" pins are hollow
A run into another county is at a foreign address, but the geocoder still biases toward the sending county. Measured across 982 of them, 70% land closer to the sender than to the destination — so those pins are unreliable by construction and are drawn as open circles. The transcripts are still exact.
Every pin is boundary-checked
Addresses come from scanner transcripts, so many do not geocode cleanly. Each pin is tested point-in-polygon against US Census county boundaries and only drawn when it really falls inside the county the call is attributed to. Calls that fail are still listed, labelled with the county they wrongly resolved to, but never drawn on the map.
In September 2026 we re-geocoded the historical backlog behind this — 73,196 distinct addresses re-run through the current pipeline, correcting 62,669 stored coordinates that had resolved outside their own county, which moved 232 more of these incidents onto the map. Coordinates that still could not be resolved were left alone rather than blanked, so no alert lost its pin.
Most failures are Baltimore City / Baltimore County confusion on street names that straddle the line, plus a geocoder sink that drops Baltimore addresses into St. Mary's County. When the geocoder gives up entirely it returns a county centroid, so a dense dot is not always a dense block.
What is not here
We record the radio of seven counties — Baltimore City, Baltimore County, Anne Arundel, Howard, Harford, Cecil and Queen Anne's. Cecil and Queen Anne's came online in late August 2026 and logged no mutual aid of their own before the window closed, so they appear here only as partners; that is a quiet few weeks, not a gap in coverage.
Carroll, York County PA, Prince George's, Montgomery and Calvert are genuinely not recorded — they show up only when a county we do record names them, so their own needs are invisible rather than absent. And aid arranged by phone or CAD never reaches the air at all, so no amount of listening would catch it.
Source
Every dispatch transcript in the Maryland Alerts pipeline since 1 January 2026, re-read and deduplicated every morning. Times are Eastern. Transcripts are machine-generated from scanner audio and contain recognition errors. Independent project — not affiliated with any fire department or government agency.