[Maps] use geo_hex grid aggregation for heatmap layer

[nreese]

Now that geohex_grid aggregation supports geo_shape (added in 8.7), Maps should add support for heatmap layers to use geohex_grid aggregation.

Should aggregation choice be exposed to the user through the UI?

• Arguments against exposing aggregation in UI:
  • avoid UI complexity and overwhelming users with complex choices they don't understand or care about
• Arguments for exposing aggregation in UI:
  • geohex_grid aggregation is currently slower then geotile_grid aggregation so heatmap layer my be slower with geohex_grid aggregation.
  • geohex_grid aggregation is a licensed feature for on prem. On prem users without a subscrition would have to fall back to geotile_grid aggregation.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[nreese]

Started working on a POC implementation and LOE is higher than anticipated, more likely a few days. Hard part is properly setting heatmap-radius for hexagons. Current implementation for grid tiles uses hard coded values based on resolution. This will not work for hexagons because hexagon radius does not scale 1:1 with zoom level, and hexagon radius increases as latitudes get closer to poles.

Chatted with @iverase about the issue and Ignacio suggested setting heatmap-radius to radius of hexagon. This is possible since heatmap-radius supports expressions and feature-state.

Hexagon feature provided by Elasticsearch vector tile does not contain this radius. Radius would have to be calculated and converted to pixels and added to feature-state to be available in expressions.

[nreese]

In order to provide better transparency of priorities, issues that will not be prioritized within the next 24 months are being closed.

Tracking request in Maps ice box #154870