Cross-filtering

The map and the rest of the dashboard talk to each other through dashboard variables. Add a variable, map something to it under Cross-filtering, and the map becomes a control for every other panel.

There are four kinds of mapping, and they behave quite differently.

Source	Direction	What lands in the variable
Filter	map ↔ variable	the value of a kepler filter
Click	map → variable	the clicked entity's value of a column
Coordinates	map → variables	the clicked place, as a lat/lng pair
Center	variables → map	nothing; it reads a pair and moves the viewport

Why variables and not Grafana's own cross-filtering

Because a variable is read from the URL, which has two consequences that matter.

The map reacts to a variable even when its own query never mentions it — so you can filter the map from a dropdown, a text box, or a data link on a table row, without the map re-querying. And a shared link carries the state: send someone a URL and they see the filter you were looking at.

Filter — the two-way one

The default. Pick a column and a variable; a select, multi-select or text filter set on that column in kepler's filter panel writes its value to the variable, and changing the variable applies the matching filter back on the map.

Cross-filtering
  Field:    vehicle_type
  Variable: $vehicle_type

Now filtering the map to buses filters every panel whose query says WHERE type IN ($vehicle_type), and picking buses from the variable picker filters the map.

Numeric ranges

Name a second variable and the mapping becomes a range mapping: a numeric range filter on the column publishes its bounds as a min/max pair, exactly the way the time window does.

WHERE speed BETWEEN $speed_min AND $speed_max

When the filter is removed, both variables are written blank rather than left holding their old values. That is deliberate: with the map at "no filter" and the variables at the old pair, neither side would ever match the last agreement again and the variables could never drive the map again.

The "All" value

Grafana's $__all and the empty string are both read as "no value", so a multi-value variable set to All clears the filter rather than filtering for the literal string $__all.

Click — publish the entity

Switch a mapping's source to Click. Now clicking a point or a trajectory writes that entity's value of the column into the variable.

-- on any consuming panel
WHERE vehicle_id = '$vehicle'

One way only, map → variable. Clicking empty map clears the variable — but only when the running selection was published from this panel, so a shared link's preset value survives a stray click on the sea.

Coordinates — publish the place

Switch a mapping's source to Coordinates. Instead of a column value, the pair of variables named under Lat and Lng receives the coordinate that was clicked.

That is what lets another panel run a spatial query around the click, with $radius an ordinary dashboard variable:

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

The computed coverage comes back to the map as one more query, so the panel needs no spatial logic of its own.

How pinning works

The panel switches kepler's coordinate interaction on by itself for this — and switches it back on if you turn it off, since the mapping would otherwise silently stop working.

Any click pins the coordinate. Clicking again unpins it on the map, but the variables keep the last spot until the next pin, so the consuming query never loses its centre and never runs with an empty geometry.

While the draw toolbar is engaged, clicks belong to the drawing and publish nothing.

Values are rounded to six decimal places, about 0.1 m — enough that re-pinning the same spot does not rewrite the variable and re-run the dashboard.

Center — read a pair back

Switch a mapping's source to Center and the same kind of pair works the other way: when the variables change from outside the map, the viewport centres on them, optionally jumping to the zoom level named in the mapping.

This is what turns a table into a map control. Give the table's query the coordinates as hidden columns and a per-row data link that writes them:

?var-lat=${__data.fields.latitude}&var-lng=${__data.fields.longitude}

Clicking a row flies the map to that feature. A pair of text boxes works the same way.

Two behaviours keep it sane: the map's own clicks are recognised and never re-centre it, and on load the saved viewport wins — the pair moves the map only when someone changes it.

Combining them

The four kinds are exclusive per mapping row, but a panel can have several rows. A common arrangement is a Click mapping for the entity, a Coordinates mapping for spatial queries, and a Filter mapping for a category — three rows, three variables, one map driving the whole dashboard.

Select from the popup

On a map where selecting is cheap, a click that publishes straight away is exactly right. On a map where it reloads a tab, re-runs a heavy query or swaps a whole dashboard's worth of panels, it makes looking expensive — and a reader who cannot look without committing stops exploring.

Turn on Select from the popup, under Cross-filtering, and the click is split in two: it opens kepler's popup with the entity's details and publishes nothing. The popup's Select button is what writes the variables, and Clear is what empties them.

The option appears once the panel has a Click mapping, or a drawn-area variable with Click to set the area on — those are the channels a click would otherwise publish.

It also tells you what is already selected

The popup knows whether the entity showing is the one the variables already hold, so the button reads as a selection rather than as a suggestion.

Seeing what is selected

Whatever the click channels have published is ringed on the map in amber: a ring around a selected point, an outline around a selected polygon or path. It needs no configuring — a panel with a click mapping has it.

Three things about it are deliberate:

• It is read from the variables, not from kepler's clicked entity. kepler forgets what was clicked on every data refresh, and never knew it at all on a dashboard opened from a link. The variables survive both, so the halo does too — which is what makes a shared link show which entity the numbers beside the map are about.
• No click can land on it. The rings are drawn above every layer so they are never buried, and they are deaf to the pointer, so clicking a ringed feature still hits the feature.
• It follows the columns, not one mapping. A panel that maps both a zone and a station rings the selected station and every row of the selected zone — the union, which is what a reader expects from two filters at once.

In a split map it is drawn only in the pane where the layer it belongs to is visible.

What else the map can publish

The bounding box of the current view, and any polygon you draw on it — see Publishing the viewport and drawn areas.