Adding overlapping annotations to map - ios

Question

I have an array of coordinates and I already know how to add it on a map as annotations.
What I'd like to do now is the following:
each annotation should be a red circle (no pins) that represents a fixed radius of 1 Km around the coordinates. That means that if I zoom in or out the map, the circle should adjusts itself to always represent a 1 Km radius;
if two or more circles overlaps, their color intensity should increase. For example, three or four overlapping circles will produce a solid red circle.
That's all. I have no idea where to start with this, so any help will be greatly appreciated.

Answer 1

For starter you can use below code but you will have to tweak it little to make it of your use:
in .h file confirm to MKMapViewDelegate
#interface MapViewController : UIViewController <MKMapViewDelegate>
Then,
in "viewDidLoad"
CLLocationCoordinate2D center = {X cordinate, Y cordinate};
//--> Add overlay
MKCircle *mCircle = [MKCircle circleWithCenterCoordinate:center radius:1000]; //set radius as per your need
[self.mapView addOverlay:mCircle];
Then,
- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id<MKOverlay>)overlay
{
MKCircleView *cirView = [[MKCircleView alloc] initWithOverlay:overlay];
[cirView setFillColor:[UIColor redColor]];
[cirView setStrokeColor:[UIColor blackColor]];
[cirView setAlpha:0.3f];
return cirView;
}
I think this should get you started.