class BaseClass { public Vector2 position = new Vector2(){X=0,Y=0}; }
class Class:BaseClass { public new Vector2 position = new Vector2(){X=10,Y=10}; }

BaseClass c = new Class();
// c.position.X is now 0

new

class BaseClass {
    public virtual Vector2 Position {
        get { return new Vector2(){X=0,Y=0}; }
    }
}

class Class : BaseClass {
    public override Vector2 Position {
        get { return new Vector2(){X=10,Y=10}; }
    }
}

class BaseClass {
    private Vector2 _position;
    public BaseClass() {
        _position = new Vector2(){X=0,Y=0};
    }
    protected BaseClass(Vector2 initialPosition) {
        _position = initialPosition;
    }
    public Vector2 Position {
        get { return _position; }
        set { _position = value; }
    }
}

class Class : BaseClass {
    public Class() : base(new Vector2(){X=10,Y=10}) {
    }
}