Maybe could you have a look at this extension and this feature : Extensions/dynamicTerrainDocumentation.md at master · BabylonJS/Extensions · GitHub
This allows you to depict a map (ground relief) and an object map (what objects are on this relief, where, how ?) and to show all this with only 2 draw calls by rendering only the parts around the camera actual position
example : Test Babylon SP Terrain
The map is 1000 x 1000 points (pre-computed from a perlin noise function)
The object map is almost 70 000 objects.
The terrain is only a 100x100 vertex mesh, updated from the camera position and the current map data.
The visible objects are a only pool of 6000 recycled solid particles.