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Under the hood — deck.gl
You never write deck.gl props here: kepler does that, from the settings in its layer panel. But knowing which deck.gl layer is actually doing the drawing explains a lot of behaviour that is otherwise mysterious — why a layer tolerates a million rows and another does not, why nothing drapes over terrain, why clicking works the way it does.
Extracted, not recalled
The mapping below was read out of the installed @kepler.gl/layers 3.3.0-alpha.11 and cross-checked against deck.gl's own catalogue. Bundled deck.gl is 9.3.11.
Which deck.gl layer draws what
Data-driven layers
| kepler layer | deck.gl layer | Package |
|---|---|---|
| point | ScatterplotLayer | @deck.gl/layers |
| heatmap | HeatmapLayer | @deck.gl/aggregation-layers |
| grid | GridLayer (via kepler's EnhancedCpuGridLayer) | @deck.gl/aggregation-layers |
| hexagon | HexagonLayer (via kepler's EnhancedHexagonLayer) | @deck.gl/aggregation-layers |
| cluster | ScatterplotLayer inside a kepler CompositeLayer | @deck.gl/layers |
| icon | kepler's own SvgIconLayer, a CompositeLayer | @deck.gl/core |
| geojson | GeoJsonLayer | @deck.gl/layers |
| hexagonId (H3) | H3HexagonLayer, plus ColumnLayer when extruded | @deck.gl/geo-layers, @deck.gl/layers |
| s2 | S2Layer | @deck.gl/geo-layers |
| arc | ArcLayer | @deck.gl/layers |
| line | ArcLayer with getHeight: 0 | @deck.gl/layers |
| flow | FlowmapLayer — not deck.gl | @flowmap.gl/layers |
| trip | TripsLayer, plus ScenegraphLayer for a 3D model at the head | @deck.gl/geo-layers, @deck.gl/mesh-layers |
Two of those are worth pausing on.
A kepler Line is a flattened Arc. It is deck.gl's ArcLayer with the height forced to zero, not LineLayer. That is why a line layer's controls look like an arc layer's, and why the two perform identically.
A Flow layer is not deck.gl at all. It comes from flowmap.gl, a separate visgl project that the plugin bundles (Apache-2.0). That is why its settings — clustering, adaptive scales, Max Top Flows — have no equivalent anywhere else in kepler, and why the deck.gl documentation will not help you with them.
Layers configured with a URL
| kepler layer | deck.gl layer | Package |
|---|---|---|
| vectorTile | MVTLayer / TileLayer | @deck.gl/geo-layers |
| rasterTile | TileLayer with kepler's raster mesh | @deck.gl/geo-layers |
| wms | WMSLayer | @deck.gl/geo-layers |
| tile3d | Tile3DLayer | @deck.gl/geo-layers |
| bitmap | BitmapLayer | @deck.gl/layers |
| 3D | ScenegraphLayer | @deck.gl/mesh-layers |
These take a URL rather than data. Two of them a query can supply that URL for — rasterTile from a raster_url column and wms from a service and layer name — and the other four are added by hand. See Rasters, WMS services and Layers configured with a URL.
What follows from it
Volume
The layer family tells you roughly what to expect. These are orders of magnitude on ordinary hardware, not promises:
| Family | Comfortable | Why |
|---|---|---|
| Scatterplot (point, cluster) | hundreds of thousands | one quad per row; the cheapest thing deck.gl draws |
| Aggregation (heatmap, grid, hexagon) | hundreds of thousands in, few cells out | binning happens on the CPU each time the parameters change |
| Arc / line | tens of thousands | each arc is tessellated into segments |
| GeoJSON | depends entirely on vertex count | a hundred detailed boundaries can outweigh a million points |
| Trip | tens of thousands of points | the whole path is uploaded; animation is a shader uniform |
| Flow | capped at 5,000 displayed by default | Max Top Flows; see Flows |
The binding constraint is usually transport, not rendering: every row travels from the data source through Grafana into the browser as JSON before deck.gl sees it. Aggregating in SQL is almost always cheaper than aggregating in a layer.
Nothing drapes over terrain
deck.gl draws in its own coordinate system, at the altitude your data specifies, over whatever the base map happens to be showing. The relief in the two terrain base maps belongs to MapLibre; deck.gl has no knowledge of it.
So a path across a valley floats at its nominal height rather than following the ground, and a polygon on a mountainside cuts through it. This is not a bug in the styles and there is no setting for it. See Base maps and relief.
Altitude is height above the ground
A path's third coordinate is metres above ground level, not above sea level. Map an elevation column of 2,650 m and the trace is drawn 2.65 km up — visible from far away, gone once the camera descends below it.
That is why the panel's altitude role has no autodetected column names. See Field roles.
Picking
Clicks and hovers work by colour picking: deck.gl renders an off-screen frame in which every feature has a unique colour, then reads the pixel under the pointer. It is exact rather than geometric, and it costs one extra render pass.
Two consequences worth knowing when you build a click-driven dashboard:
- What you click is what is drawn. A point with radius 1 is a one-pixel target. Raise the radius before concluding that click publishing is broken.
- Only the topmost feature is picked. Overlapping layers hand you the one on top, which is the one highest in the layer list.
See Cross-filtering.
Precision
kepler's documentation lists a High-precision rendering when zooming in closely switch on seven layer types. In the version this plugin bundles it is not wired to anything: it survives as a constant and a TypeScript type in kepler 3.3.0-alpha.11, and no layer declares or reads it.
deck.gl retired the separate 64-bit code path years ago; its current handling shifts coordinates relative to the viewport centre and is always on. There is nothing to enable, and nothing to pay for.
This is a case where upstream documentation is ahead of, or behind, what ships.
Trail length
Trail Length on a Trip layer is deck.gl's trailLength on TripsLayer, and kepler multiplies the value you type by 1,000 before handing it over. kepler exposes the control but does not document it; deck.gl documents the prop but not the multiplier.
Two WebGL contexts per map
Each map holds one context for MapLibre and one for deck.gl. Browsers cap the total at around sixteen, so roughly eight maps per page — fewer with split views, which double a map's allocation.
Past the cap the browser evicts the oldest context and those maps go black, with Too many active WebGL contexts in the console. Collapsed Grafana rows are the mitigation; see Map settings.
Reading further
deck.gl's own documentation, for when this page stops being enough: