Shows a race condition in MapKit. You cannot rely on the map.CenterCoordinate in synchronous code, and it's not clear to me what event (if any) is associated with the `UIMapView.CenterCoordinate` becoming set.

gistfile1.cs

var map = new MKMapView();

var ctr = new CLLocationCoordinate2D(37.8, -122.4);
map.SetCenterCoordinate(ctr, false);
map.SetRegion(new MKCoordinateRegion(ctr, new MKCoordinateSpan(0.025, 0.025)), false);
Console.WriteLine("Center coordinate is still NaN: " + map.CenterCoordinate.Latitude.ToString());

/*
Error: NaN Lat & Long var 
circle = MKCircle.Circle(map.CenterCoordinate, 100);

Must use explicit location instead, a la:
*/
var circle = MKCircle.Circle(ctr, 100);
      
map.AddOverlay(circle);