Terrain.heightmapMaximumLOD
var heightmapMaximumLOD: int;
int heightmapMaximumLOD;
heightmapMaximumLOD as int
Description

Lets you essentially lower the heightmap resolution used for rendering.

This can be used on low end cards to never display the highest lod terrain. A value of 0 means always showing highest detail. A value of 1 means the triangle count will be reduced to 1/4th. The heightmap resolution will be halved for width and height.
	function Start () {
		Terrain.activeTerrain.heightmapMaximumLOD = 1;
	}
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Start() {
        Terrain.activeTerrain.heightmapMaximumLOD = 1;
    }
}
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Start() as void:
		Terrain.activeTerrain.heightmapMaximumLOD = 1