class SeededRandom
    {
        private int seed;
        private Random rand;



        public SeededRandom()
        {
            Random seedR = new Random();
            seed = seedR.Next();
            rand = new Random(seed);
        }

        public SeededRandom(int seed)
        {
            this.seed = seed;
            rand = new Random(seed);
        }


        public int GetSeed()
            { return seed; }
    }

class Map
    {
        public int map_w, map_h;
        public Tile[,] map;
        public SeededRandom rand;


        public Map(int map_w, int map_h)
        {
            this.map_w = map_w;
            this.map_h = map_h;
            map = new Tile[map_h, map_w];
            rand = new SeededRandom();
        }

        public Map(int map_w, int map_h, int seed) : this(map_w, map_h)
        {
            rand = new SeededRandom(seed);
        }

        public int GetSeed()
            { return rand.GetSeed(); }
    }

class BasicRandomMap : Map
    {

        public BasicRandomMap(int map_w, int map_h) : base(map_w, map_h) { }
        public BasicRandomMap(int map_w, int map_h, int seed) : base(map_w, map_h, seed) { }
    }


class Program
    {
        static void Main(string[] args)
        {

            Map map1 = new Map(10, 10);
            Map map2 = new Map(20, 20, map1.GetSeed());
            BasicRandomMap map3 = new BasicRandomMap(10, 10);
            BasicRandomMap map4 = new BasicRandomMap(20, 20, map3.GetSeed());
            Console.WriteLine(map1.GetSeed());
            Console.WriteLine(map2.GetSeed());
            Console.WriteLine(map3.GetSeed());
            Console.WriteLine(map4.GetSeed());
        }
    }
################
Result:
1424215421
1424215421
1424215421
1424215421