How can i calculate distance on Image in a pictureBox ?

Question

This is a screenshot of what i mean:
In the screenshot i have a cone. The cone is moving around 360 degrees.
In the form1 top i have this:
private float distanceFromCenterKm = 200F; //in kilometers
private float distanceFromCenterPixels; //in pixels 183pixels = 200Km
Now in the constructor i did:
numericUpDown1.Value = 260.5M;
So now the distance is 300km
Then:
//initialize distanceFromCenterPixels
distanceFromCenterPixels = (float)(/*183d*/ (double)numericUpDown1.Value * (double)distanceFromCenterKm / 200d);
The numericupdown1 in the designer set the minimum value to 50 and maximum to 300 in jumps of 50.
But now what i don't know is how to calculate the distance for example from the center to where the shadow start you can see in the screenshot that the shadow i mean just a bit before the 300km start. So i want that the cone will get untill the start of
the shadow border. I'm close and i could keep playing with the values but how can i make that the numericupdown1 values will jump not by 50 but by some value/s so i can calculate easy any distance to any point ?
Or something else maybe something like i'm using my mouse cursor when i make a click on a point some where in the image the cone will get to this distance(radius).
So if i clicked with the mouse on the 300km on the image the value of the numericupdown will change to 260.5
And if i clicked on the shadow border(will be hard to click exactly on the border) the cone will get to this distance.
But my main question/problem is how to calculate any distance for example to this shadow border ?

Answer 1

You simply should not go this way.
Get a Map SDK and go on. 
Microsoft has one. Probably for you is the best one the WPF one. AFAIK has it classes which you probably also can incorporate in your Windows Forms solution to get the Geo Information.
https://msdn.microsoft.com/en-us/library/hh750210.aspx
Success
Cor