Boilerplate MKMapView annotation view creation and update based on map region.

MKMapKit_Annotations.m

# pragma mark - 
# MapView Delegate methods

- (void)mapView:(MKMapView *)map regionDidChangeAnimated:(BOOL)animated
{
    NSArray *oldAnnotations = mapView.annotations;
    [mapView removeAnnotations:oldAnnotations];
 
    NSArray *weatherItems = [weatherServer weatherItemsForMapRegion:mapView.region maximumCount:4];
    [mapView addAnnotations:weatherItems];
}
 
- (MKAnnotationView *)mapView:(MKMapView *)map viewForAnnotation:(id <MKAnnotation>)annotation
{
    static NSString *AnnotationViewID = @"annotationViewID";
        
    WeatherAnnotationView *annotationView =
            (WeatherAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:AnnotationViewID];
    if (annotationView == nil)
    {
        annotationView = [[[WeatherAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:AnnotationViewID] autorelease];
    }
    
    annotationView.annotation = annotation;
    
    return annotationView;
}

# pragma mark -
# MKAnnotation protocol

@interface

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;

@end

@implementation

- (CLLocationCoordinate2D)coordinate
{
    coordinate.latitude = [self.latitude doubleValue];
    coordinate.longitude = [self.longitude doubleValue];
    return coordinate;
}

 @end