Procedural terrain code

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.Mathematics;
using System;
using Unity.VisualScripting;
using Unity.VisualScripting.Dependencies.Sqlite;

public class TerrainGenerator : MonoBehaviour
{
    public int TextureSize;
    public int xSize = 20;
    public int zSize =20;
    public float NoiseScale, IslandSize;
    [Range(1, 20)] public int NoiseOctaves;


    // Privates

    Color[] col;
    Texture2D tex;
    int Seed;
    Mesh mesh;
    Vector3[] vertices;
    Vector2[] uvs;
    int[] triangles;
    float noiseValue;
    public Gradient ColorGradient;

    private void Start()
    {
        mesh = new Mesh();
        GetComponent<MeshFilter>().mesh = mesh;
        Seed = UnityEngine.Random.Range(0, 99999);
        tex = new Texture2D(TextureSize, TextureSize);
        col = new Color[tex.height * tex.width];

        Renderer rend = GetComponent<MeshRenderer>();
        rend.sharedMaterial.mainTexture = tex;

        Vector2 Org = new Vector2(Mathf.Sqrt(Seed), Mathf.Sqrt(Seed));

        for (int x = 0, i = 0; x < TextureSize; x++)
        {
            for (int y = 0; y < TextureSize; y++, i++)
            {
                col[i] = ColorGradient.Evaluate(Noisefunction((float)x, (float)y, Org));
            }
        }
        tex.SetPixels(col);
        tex.Apply();
        tex.wrapMode = TextureWrapMode.Clamp;
    }

    private void Update()
    {
        CreateShape();
        UpdateMesh();
    }

    private void UpdateMesh()
    {
        mesh.Clear();
        mesh.vertices = vertices;
        mesh.triangles = triangles;
        mesh.uv = uvs;
        mesh.RecalculateNormals();
    }

    //creates the mesh
    private void CreateShape()
    {
        vertices = new Vector3[(xSize + 1) * (zSize + 1)];
        for (int z = 0, i = 0; z <= zSize; z++)
        {
            for (int x = 0; x <= xSize; x++)
            {
                vertices[i] = new Vector3(x, noiseValue, z);
                i++;
            }
        }
        triangles = new int[xSize * zSize * 6];

        int vert = 0;
        int tris = 0;
        for (int z = 0; z < zSize; z++)
        {
            for (int x = 0; x < xSize; x++)
            {
                triangles[tris + 0] = vert + 0;
                triangles[tris + 1] = vert + xSize + 1;
                triangles[tris + 2] = vert + 1;
                triangles[tris + 3] = vert + 1;
                triangles[tris + 4] = vert + xSize + 1;
                triangles[tris + 5] = vert + xSize + 2;
                vert++;
                tris += 6;
            }
            vert++;
        }

        uvs = new Vector2[vertices.Length];
        for (int z = 0, i = 0; z <= zSize; z++)
        {
            for (int x = 0; x <= xSize; x++)
            {
                uvs[i] = new Vector2((float)x / xSize, (float)z / zSize);
                i++;
            }
        }
    }


    //creates noise
    private float Noisefunction(float x, float y, Vector2 Origin)
    {
        float a = 0, noisesize = NoiseScale, opacity = 1;

        for (int octaves = 0; octaves < NoiseOctaves; octaves++)
        {

            float xVal = (x / (noisesize * TextureSize)) + Origin.x;
            float yVal = (y / (noisesize * TextureSize)) - Origin.y;
            noiseValue = noise.snoise(new float2(xVal, yVal)); // thought this was the line to get the noise value
            a += Mathf.InverseLerp(0, 1, noiseValue) / opacity;

            noisesize /= 2f;
            opacity *= 2f;
        }

        return a -= FallOffMap(x, y, TextureSize, IslandSize);
    }

    //makes it an island
    private float FallOffMap(float x, float y, int size, float islandSize)
    {
        float gradient = 1;

        gradient /= (x * y) / (size * size) * (1 - (x / size)) * (1 - (y / size));
        gradient -= 16;
        gradient /= islandSize;


        return gradient;
    }
}