Fast Terrain Scanning

TerrainScanner.cs

using System.Collections.Generic;
using Unity.Collections;
using UnityEngine;

[System.Serializable]
public class Tile
{
    public int Key;
    public Vector3 Position;
    public Vector3 Normal;
    public float Elevation;
    public bool Sloped;

    public Tile (int key, Vector3 position, Vector3 normal, bool sloped)
    {
        Key = key;
        position.y = Elevation = Mathf.Round (position.y * 10) / 10;
        Normal = normal;
        Position = position;
        Sloped = sloped;
    }
}

public class TerrainScanner : MonoBehaviour
{
    public Dictionary<int, Tile> TilePositions = new Dictionary<int, Tile> ();
    public LayerMask raycastMask;
    public Vector2Int MapSize = new Vector2Int (512, 512);

    private void Start ()
    {
        MapTerrain ();
    }

    public void MapTerrain ()
    {

        var sw = new System.Diagnostics.Stopwatch ();
        sw.Start ();

        TilePositions.Clear ();

        var commandSize = (MapSize.x * MapSize.y);
        var up = Vector3.up;
        var down = Vector3.down;
        var hits = 1;
        var results = new NativeArray<RaycastHit> (commandSize * hits, Allocator.Temp);
        var commands = new NativeArray<RaycastCommand> (commandSize, Allocator.Temp);

        for (int x = 0; x < MapSize.x; x++)
        {
            for (int y = 0; y < MapSize.y; y++)
            {
                var key = GetKey (x, y);
                var origin = new Vector3 (x, 200, y);
                commands[key] = new RaycastCommand (origin, down, 300, raycastMask, hits);
            }
        }

        var handle = RaycastCommand.ScheduleBatch (commands, results, MapSize.x);
        handle.Complete ();
        commands.Dispose ();

        for (int x = 0; x < MapSize.x; x++)
        {
            for (int y = 0; y < MapSize.y; y++)
            {
                var position = new Vector3 (x, 0, y);
                position.y = 0;
                var key = GetKey (x, y);
                var result = results[key];
                var isSloped = false;
                var normal = up;

                if (result.collider)
                {
                    position = result.point;
                    normal = result.normal;
                    isSloped = normal != up;
                }

                var tile = new Tile (key, position, normal, isSloped);
                TilePositions[key] = tile;
            }
        }
        results.Dispose ();
        sw.Stop ();
        Debug.Log ("Scanning done in " + sw.ElapsedMilliseconds + "ms");
    }

    public Tile GetTileAtPosition (Vector3 position)
    {
        if (TilePositions.Count == 0) return null;
        var x = Mathf.RoundToInt (position.x);
        var z = Mathf.RoundToInt (position.z);
        var key = GetKey (x, z);
        if (!TilePositions.ContainsKey (key)) return null;
        return TilePositions[key];
    }

    int GetKey (int x, int y)
    {
        return x * MapSize.x + y;
    }
}

For a 512 x 512 terain:
Scanning done in 176ms

Minimum Unity Version: 2018.1
Set project to use .net 4
Install the entities package from the Package Manager