TreehouseDefense.map does not contain a definition for OnMap

using System;
namespace TreehouseDefense
{
    class Game
    {
        public static void Main()
        { 
            Map map = new Map(8, 5);

            Point point = new Point(4, 2);
            bool isOnMap = map.OnMap(point);
            Console.WriteLine(isOnMap);

            point = new Point(8, 5);
            isOnMap = map.OnMap(point);
            Console.WriteLine(isOnMap);
        }
    }
}

namespace TreehouseDefense
{
    class Map
    {
        public readonly int Height;
        public readonly int Width;

      public Map(int width, int height)
      {
        Height = height;
        Width = width;
      }

      public bool onMap (Point point)
      {
        return point.X >= 0 && point.X < Width &&
               point.Y >= 0 && point.Y < Height;
      }
    }
}