I have to represent graphically an oriented graph like in the image below.

i have a C# form, when i click with the mouse on it i have to draw a node. If i click somewhere on the form where is not already a node drawn it means i cliked with the intetion of drawing a node, if it is a node there i must select it and memorize it. On the next mouse click if i touch a place where there is not already a node drawn it means like before that i want to draw a new node, if it is a node where i clicked i need to draw the line from the first memorized node to the selected one and add road cost details.

i know how to draw the circles that represent the nodes of the graph when i click on the form. i'm using the following code:

namespace RepGraficaAUnuiGraf
{
    public partial class Form1 : Form
    {
        Graphics graphDrawingArea;
        Bitmap bmpDrawingArea;
        Graphics graph;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            bmpDrawingArea = new Bitmap(Width, Height);
            graphDrawingArea = Graphics.FromImage(bmpDrawingArea);
            graph = Graphics.FromHwnd(this.Handle);
        }

        private void Form1_Click(object sender, EventArgs e)
        {          
            DrawCentralCircle(((MouseEventArgs)e).X, ((MouseEventArgs)e).Y, 15);
            graph.DrawImage(bmpDrawingArea, 0, 0);
        }

        void DrawCentralCircle(int CenterX, int CenterY, int Radius)
        {
            int start = CenterX - Radius;
            int end = CenterY - Radius;
            int diam = Radius * 2;
            bmpDrawingArea = new Bitmap(Width, Height);
            graphDrawingArea = Graphics.FromImage(bmpDrawingArea);
            graphDrawingArea.DrawEllipse(new Pen(Color.Blue), start, end, diam, diam);
            graphDrawingArea.DrawString("1", new Font("Tahoma", 13), Brushes.Black, new PointF(CenterX - 8, CenterY - 10));
        }

    }
}

My question is how can i find out if at the coordinates (x,y) on my form i drew a node and which one is it? I thought of representing the nodes as buttons, having a tag or something similar as the node number(which in drawing should be 1 for Santa Barbara, 2 for Barstow etc.)