Bakes the terrain into a TVE colormap (requires AllTerrainTextures & The Vegetation engine assets)

TerrainBaker.cs

using UnityEngine;
using AmazingAssets.AllTerrainTextures;

#if THE_VEGETATION_ENGINE
using TheVegetationEngine;
#endif

#if UNITY_EDITOR
using UnityEditor;
#endif

namespace OneFoxStudio.Utilities
{
    [ExecuteInEditMode]
    public class TerrainBaker : MonoBehaviour
    {
        [SerializeField] private int terrainSize = 128;
        [SerializeField] private int terrainResolution = 1024;
        [SerializeField] private Shader colorMapElementShader;
        [SerializeField] private Color colormapColor;
        [SerializeField] private Mesh QuadMesh;

        [SerializeField] private string assetsPath = "Assets/_Game/Terrain/";
        private Terrain[] terrains;

        private void Clear()
        {
            terrains = FindObjectsOfType<Terrain>();
            foreach (var terrain in terrains)
            {
#if THE_VEGETATION_ENGINE
                var elements = terrain.gameObject.GetComponentsInChildren<TVEElement>();
                foreach (var e in elements)
                    DestroyImmediate(e.gameObject);
#endif
            }
        }

        private void BakeTerrain()
        {
#if UNITY_EDITOR
            Clear();

            terrains = FindObjectsOfType<Terrain>();

            foreach (var terrain in terrains)
            {
                var terrainTransform = terrain.transform.position;
                var terrainPosition = new Vector2(terrainTransform.x, terrainTransform.z);
                var colorMapTexture = Bake(terrain);
                SaveTextureAsPNG(colorMapTexture,
                    assetsPath + $"ColorMap/ColorMap[{terrainPosition.x},{terrainPosition.y}].png");
                var colorMapMaterial = new Material(colorMapElementShader);
                AssetDatabase.CreateAsset(colorMapMaterial,
                    assetsPath + $"ColorMap/Colormap[{terrainPosition.x},{terrainPosition.y}].mat");
                colorMapMaterial.name = $"Colormap[{terrainPosition.x},{terrainPosition.y}]";
                colorMapMaterial.SetTexture("_MainTex", colorMapTexture);
                colorMapMaterial.SetColor("_MainColor", colormapColor);
                colorMapMaterial.SetFloat("_MainTexAlphaMinValue", 0f);
                colorMapMaterial.SetFloat("_MainTexAlphaMaxValue", 0f);
                var colorMap = new GameObject();
                colorMap.name = $"Colormap[{terrainPosition.x},{terrainPosition.y}]";
                colorMap.AddComponent<MeshFilter>().mesh = QuadMesh;
                colorMap.AddComponent<MeshRenderer>().sharedMaterial = colorMapMaterial;
                colorMap.GetComponent<MeshRenderer>().shadowCastingMode = UnityEngine.Rendering.ShadowCastingMode.Off;
                colorMap.GetComponent<MeshRenderer>().receiveShadows = false;
                var t = (Texture2D)AssetDatabase.LoadAssetAtPath(
                    assetsPath + $"ColorMap/ColorMap[{terrainPosition.x},{terrainPosition.y}].png", typeof(Texture2D));
                colorMap.AddComponent<TVEElement>();

                colorMap.GetComponent<TVEElement>().elementRenderer.sharedMaterial.mainTexture = t;

                colorMap.transform.parent = terrain.transform;
                colorMap.transform.localPosition = new Vector3(terrainSize / 2, -0.01f, terrainSize / 2);
                colorMap.transform.localScale = new Vector3(terrainSize, 1f, terrainSize);
                AssetDatabase.SaveAssets();
            }

            AssetDatabase.Refresh();
#endif
        }

        private Texture2D Bake(Terrain terrain)
        {
            if (terrain == null) Debug.LogError("Terrain is null");
            Texture2D colorMap;
            colorMap = terrain.terrainData.AllTerrainTextures(false, false).Basemap.Diffuse(terrainResolution);
            return colorMap;
        }

        private static void SaveTextureAsPNG(Texture2D _texture, string _fullPath)
        {
            var bytes = _texture.EncodeToPNG();
            System.IO.File.WriteAllBytes(_fullPath, bytes);
        }

        public void Bake()
        {
            BakeTerrain();
        }
    }
}

TerrainBakerEditor.cs

using UnityEditor;
using UnityEngine;

namespace OneFoxStudio.Utilities
{
    [CustomEditor(typeof(TerrainBaker))]
    public class TerrainBakerEditor : Editor
    {
        public override void OnInspectorGUI()
        {
            base.OnInspectorGUI();
            var t = (TerrainBaker)target;

            if (GUILayout.Button("Bake"))
                t.Bake();
        }
    }
}

Shader: Pick the ColorMap shader from TVE
Terain size & resolution: Adjust your terrain size & resolution
ColorMapColor: make it around grey (I tend to use 147 for R,G,B)
QuadMesh: pick any quad mesh (there's one in TVE)