Variable formats

Exactly what the panel writes into a dashboard variable, per channel, and how to consume it safely.

Summary

Channel	Variables	Value
Filter (scalar)	1	the filter's value, as a string
Filter (range)	2	numeric min and max, as strings
Time window	2	UTC ISO 8601
Click	1	the clicked entity's column value
Coordinates	2	latitude and longitude, 6 decimal places
Viewport	4	west, south, east, north — degrees, 6 decimal places
Drawn area	1	WKT in EPSG:4326

Everything is written as a string, because that is what a dashboard variable holds.

Time window

2026-08-18T14:30:00.000Z

UTC ISO 8601, as produced by toISOString. Chosen over epoch milliseconds because the target is usually a SQL timestamptz, and because it is legible in a URL and in a shared link.

Reading is more permissive than writing: ISO, any Date-parseable string, epoch ms as a number, or epoch ms as a numeric string. The empty string and Grafana's $__all are read as "no window".

Coordinates

Two variables — latitude in the first, longitude in the second — each a decimal degree rounded to six decimal places, about 0.1 m.

The rounding is not cosmetic: it means re-pinning the same spot does not rewrite the variable, and so does not re-run every panel that reads it.

Values survive an unpin. Clicking again unpins the marker on the map, but the variables keep the last position until the next pin, so a consuming spatial query never runs with an empty centre.

Viewport

Four variables, each a decimal degree rounded to six places:

Variable	Edge
west	minimum longitude
south	minimum latitude
east	maximum longitude
north	maximum latitude

Numbers rather than a geometry, deliberately: there is nothing free-form for a consuming query to interpolate.

Coordinates are clamped to valid ranges. Zoomed far enough out the computed span runs past the antimeridian and the poles, and no consumer should be handed a longitude of −250.

Published once on load, then 300 ms after the map comes to rest. A value that has not changed numerically is not rewritten.

Drawn area

WKT in EPSG:4326, for example:

POLYGON((-79.01 -2.91,-78.98 -2.91,-78.98 -2.88,-79.01 -2.88,-79.01 -2.91))

Only the most recent figure. Deleting the last one clears the variable to the empty string — which is what the != '' guard in every example is for.

Never written on dashboard load, so a shared link keeps the area it was opened with.

Range filters

Two variables holding the numeric bounds as strings. When the filter is removed both are written blank, rather than left holding their old values — otherwise the map would be at "no filter" while the variables held a range, and neither side would ever match the last agreement again.

Consuming safely

Guard the empty value

Every channel can be empty: before the first interaction, after a clear, or on a fresh dashboard. Panels reading the variable run anyway.

-- drawn area
WHERE $area != '' AND ST_Intersects(geom, ST_GeomFromText($area, 4326))

-- coordinates
WHERE $lat != '' AND ST_DWithin(geom, ST_MakePoint($lng, $lat)::geography, $radius)

-- time window, PostgreSQL
WHERE ('$from' = '' OR ts >= '$from'::timestamptz)

Quoting depends on the data source

Do not quote a variable on a source that interpolates with a SQL string format

Some data sources — the DuckDB one among them — add the quotes themselves. '$var' arrives as ''value'' and fails to parse. Write $var, and cast defensively:

WHERE ts >= coalesce(try_cast($from AS TIMESTAMPTZ), '-infinity')

The PostgreSQL data source does not do this; there, quote normally. When in doubt, read the generated SQL in the query inspector.

Do not consume your own map's output

Putting the viewport or the drawn area into this panel's query makes the map filter itself, and the filter cannot be widened again — the rows are gone. See Publishing.

Multi-value variables

Grafana repeats a variable in the URL when it is multi-value. Every single-valued channel here reads the first entry, so a variable that has accidentally become multi-value degrades rather than breaking.