How to draw text to an image map?

Hi all,
I have an image map with hot spots on a page. I have to draw a number with red color or blue color which depends on the value retreived from the database. I know how to draw the number but I don't know how to acces the image map or how to associate the image map to the Graphics class.
My code is below:
Graphics grf = Graphics.FromImage(ImageMap1); // I know that this line is not correct but i don't know how to write it.

        try
        {
            grf.Clear(Color.White);
            using (Font myFont = new Font("Arial", 14))
            {
                grf.DrawString("10", myFont, ...