Yes, it is rectangular. I need the approximate radius of the map rendered in that rectangular area.

Let me try & explain again:

1. The height & width of the area where the map is displayed remains constant. And the MapOptions height & width also are set to this same value -
Height = 400;
Width = 450;
mapOptions.Format.Height = Height;
mapOptions.Format.Width = Width;

2. The map is rendered using ViewByScale.
scale = 5000000;
mapViews[0].CenterPoint = latLong;
mapViews[0].MapScale = scale;

Now the map is displayed in the rectangular area. I need to know what would be the approximate radius of the map which is rendered with the scale mentioned above. Note: the scale keeps changing.

Hope the query is clear.