MapLocation parameters

As @andren points out, it is good practice to always include a reference to the code or video, but I will try to answer the question.

MapLocation is a child class of Point, and a point is located on the map. There are many scenarios in which the MapLocation class would need an instance of the Map class, I will use the following scenario as an example.

There is a method of the Map class called OnMap(). OnMap() takes in a point as a parameter, evaluates the X & Y values to see if the point is located on the map, and returns a Boolean(true or false).

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

In a constructor of the MapLocation class, the OnMap(); method is called.

public MapLocation(int x, int y, Map map) : base(x, y)
    {
      if(!map.OnMap(this))
      {
        throw new OutOfBoundsException(x + "," + y + " is outside the limits of the map.");
      }
    }

map.OnMap(this) is where the method is called, and it is passed this, which in this case represents a MapLocation object containing X & Y values. The purpose of MapLocation calling OnMap() is to determine if the current X & Y values are valid, meaning that they are located on the map. In order for the MapLocation constructor to call OnMap(), which is a public method, but located in a different class, MapLocation must take an instance of the Map class as a parameter.

Additionally, OnMap() must take in an instance of MapLocation inorder to access and evaluate the X & Y properties of the MapLocation object.

This might be a little confusing because OnMap() doesn't take MapLocation as a parameter, it takes Point as a parameter. OnMap() can also take MapLocation objects as a parameter because MapLocation is a child class that inherits from Point

class MapLocation : Point

Hope this helps.