Heatmap shows inconsistent format with different zoom level

[Peipei17]

Kibana version: 5.1.1

Elasticsearch version: 5.1

Server OS version: Linux

Browser version: Chrome, Version 56.0.2924.87 (64-bit)

Browser OS version: OSX 10.10.5

Original install method (e.g. download page, yum, from source, etc.): AWS ElasticService

Description of the problem including expected versus actual behavior:
We use Kibana TileMap to show the traffic on world map. It performs really well with Circle Marker and Geohash Grid. But the heatmap format displays in inconsistent style with different zoom level.
Please refer to the attached images as the example. The display style is kind geohash grid with zoom1. After zoom in one level, the display changes to real heatmap with hot degree. Then zoom in again, the display changes to geohash grid style again. It happens alternatively with the zoom level. The zoom level changes should not has impact on the display format.

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

[thomasneirynck]

related to #8763.

[thomasneirynck]

This is a real issue, but related to how we use Elasticsearch geohash aggregations, which do not have a uniform scale and map to individual zoom levels. imho, this would better be achieved by using a better aggregation mechanism in Elasticsearch, e.g. based on web-mercator tiles (elastic/elasticsearch#24587). Until that is available, it is unlikely we will fix this on the client-end.