title: Custom core-graphics overlay within MKMapView: can't display stroked ellipse
body: <p>I'm trying to draw a series of concentric circles as a custom overlay within a MKMapView.  Please note that for performance reasons, I need to implement a custom draw method, not simply add a series of MKCircleViews.</p>
  
  <p>I have the following code, and I have no idea why I can see the circles if they are filled, but when I just try to draw empty circles (i.e. stroke outline only), I see nothing.</p>
  
  <pre><code>- (void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context {
  // draw series of concentric circles
  
  // I have tried all manner of line widths
  CGContextSetLineWidth(context, 5.0);
  
  CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor); 
  CGContextSetStrokeColorWithColor(context, [UIColor yellowColor].CGColor); 
  
  float radius;
  
  for (int i = 1; i &lt; self.numberOfRings+1; i++) {
  
      //  code to calculate the radius here using i
      // but this is fine, set to 1000 metres
      radius = 1000.0;
  
      // centre of circles
      CLLocationCoordinate2D centre = {latitude: self.latitude, longitude: self.longitude};
  
      // create circle of appropriate geographical dimensions
      MKCircle *circle = [MKCircle circleWithCenterCoordinate:centre radius:radius];
  
      // the next two lines don't work, I don't see anything drawn
      CGContextStrokeEllipseInRect(context, [self rectForMapRect:[circle boundingMapRect]] );
      CGContextStrokePath(context);
  
      // but the dimensions of the rect are ok, because I see the filled in rect (below) perfectly if I uncomment this next line
      //      CGContextFillEllipseInRect(context, [self rectForMapRect:[circle boundingMapRect]] );
  
      }
  }
  </code></pre>
  
  <p>Please, what on earth am I supposed to do to get the stroked images to display?</p>