how to use custom coordinates for drawing lines or points

Hi all,
I am new at GDI and graphics and will like some help trying to draw lines or plot points.
I have the following code and do not understand why the line is not drawn? 

using System;
using System.Drawing;
using System.Windows.Forms;
namespace lineplot
{
    public partial class Form1 : Form
    {
        private Rectangle drawingRectangle;
        private float xMin = 500000f;
        private float xMax = 600000f;
        private float yMin = 5000000f;
        private float yMax = 6000000f;
        private int offset = 10;

        public Form1()
        {
            InitializeComponent();
            this.SetStyle(ControlStyles.ResizeRedraw, true);
            this.BackColor = Color.White;
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            Rectangle rect = ClientRectangle;
            drawingRectangle = new Rectangle(rect.Location, rect.Size);
            drawingRectangle.Inflate(-offset, -offset);
            g.DrawRectangle(Pens.Red, rect);
            g.DrawRectangle(Pens.Black, drawingRectangle);
            Pen aPen = new Pen(Color.Green, 3);
            g.DrawLine(aPen, Point2D(new PointF(695312, 5668062)),
                Point2D(new PointF(695312, 5668100)));
            aPen.Dispose();
            g.Dispose();
        }

        private PointF Point2D(PointF ptf)
        {
            PointF aPoint = new PointF();
            aPoint.X = drawingRectangle.X + (ptf.X - xMin) *
                drawingRectangle.Width / (xMax - xMin);
            aPoint.Y = drawingRectangle.Bottom - (ptf.Y - yMin) *
                drawingRectangle.Height / (yMax - yMin);
            return aPoint;
        }
    }
}<pre lang="c#">