Сгруппированы/разгруппированы MKAnnotation в зависимости от уровня масштабирования (и сохраняйте скорость)

Посмотрите здесь, чтобы увидеть полный ответ. Он содержит обе реализации для MapKit и Google Maps. Код вдохновлен видео WWDC 2011 и очень хорошо работает в моем приложении.

Я все равно размещаю здесь код для MapKit, но в моем другом ответе есть несколько полезных замечаний.

- (void)didZoom:(UIGestureRecognizer*)gestureRecognizer {
    if (gestureRecognizer.state == UIGestureRecognizerStateEnded){
        [self updateVisibleAnnotations];
    }
}
- (void)updateVisibleAnnotations {
    static float marginFactor = 2.0f;
    static float bucketSize = 50.0f;
    MKMapRect visibleMapRect = [self.mapView visibleMapRect];
    MKMapRect adjustedVisibleMapRect = MKMapRectInset(visibleMapRect, -marginFactor * visibleMapRect.size.width, -marginFactor * visibleMapRect.size.height);

    CLLocationCoordinate2D leftCoordinate = [self.mapView convertPoint:CGPointZero toCoordinateFromView:self.view];
    CLLocationCoordinate2D rightCoordinate = [self.mapView convertPoint:CGPointMake(bucketSize, 0) toCoordinateFromView:self.view];
    double gridSize = MKMapPointForCoordinate(rightCoordinate).x - MKMapPointForCoordinate(leftCoordinate).x;
    MKMapRect gridMapRect = MKMapRectMake(0, 0, gridSize, gridSize);

    double startX = floor(MKMapRectGetMinX(adjustedVisibleMapRect) / gridSize) * gridSize;
    double startY = floor(MKMapRectGetMinY(adjustedVisibleMapRect) / gridSize) * gridSize;
    double endX = floor(MKMapRectGetMaxX(adjustedVisibleMapRect) / gridSize) * gridSize;
    double endY = floor(MKMapRectGetMaxY(adjustedVisibleMapRect) / gridSize) * gridSize;

    gridMapRect.origin.y = startY;
    while(MKMapRectGetMinY(gridMapRect) <= endY) {
        gridMapRect.origin.x = startX;
        while (MKMapRectGetMinX(gridMapRect) <= endX) {
            NSSet *allAnnotationsInBucket = [self.allAnnotationMapView annotationsInMapRect:gridMapRect];
            NSSet *visibleAnnotationsInBucket = [self.mapView annotationsInMapRect:gridMapRect];

            NSMutableSet *filteredAnnotationsInBucket = [[allAnnotationsInBucket objectsPassingTest:^BOOL(id obj, BOOL *stop) {
                BOOL isPointMapItem = [obj isKindOfClass:[PointMapItem class]];
                BOOL shouldBeMerged = NO;
                if (isPointMapItem) {
                    PointMapItem *pointItem = (PointMapItem *)obj;
                    shouldBeMerged = pointItem.shouldBeMerged;
                }
                return shouldBeMerged;
            }] mutableCopy];
            NSSet *notMergedAnnotationsInBucket = [allAnnotationsInBucket objectsPassingTest:^BOOL(id obj, BOOL *stop) {
                BOOL isPointMapItem = [obj isKindOfClass:[PointMapItem class]];
                BOOL shouldBeMerged = NO;
                if (isPointMapItem) {
                    PointMapItem *pointItem = (PointMapItem *)obj;
                    shouldBeMerged = pointItem.shouldBeMerged;
                }
                return isPointMapItem && !shouldBeMerged;
            }];
            for (PointMapItem *item in notMergedAnnotationsInBucket) {
                [self.mapView addAnnotation:item];
            }

            if(filteredAnnotationsInBucket.count > 0) {
                PointMapItem *annotationForGrid = (PointMapItem *)[self annotationInGrid:gridMapRect usingAnnotations:filteredAnnotationsInBucket];
                [filteredAnnotationsInBucket removeObject:annotationForGrid];
                annotationForGrid.containedAnnotations = [filteredAnnotationsInBucket allObjects];
                [self.mapView addAnnotation:annotationForGrid];
                //force reload of the image because it's not done if annotationForGrid is already present in the bucket!!
                MKAnnotationView* annotationView = [self.mapView viewForAnnotation:annotationForGrid];
                NSString *imageName = [AnnotationsViewUtils imageNameForItem:annotationForGrid selected:NO];
                UILabel *countLabel = [[UILabel alloc] initWithFrame:CGRectMake(15, 2, 8, 8)];
                [countLabel setFont:[UIFont fontWithName:POINT_FONT_NAME size:10]];
                [countLabel setTextColor:[UIColor whiteColor]];
                [annotationView addSubview:countLabel];
                imageName = [AnnotationsViewUtils imageNameForItem:annotationForGrid selected:NO];
                annotationView.image = [UIImage imageNamed:imageName];

                if (filteredAnnotationsInBucket.count > 0){
                    [self.mapView deselectAnnotation:annotationForGrid animated:NO];
                }
                for (PointMapItem *annotation in filteredAnnotationsInBucket) {
                    [self.mapView deselectAnnotation:annotation animated:NO];
                    annotation.clusterAnnotation = annotationForGrid;
                    annotation.containedAnnotations = nil;
                    if ([visibleAnnotationsInBucket containsObject:annotation]) {
                        CLLocationCoordinate2D actualCoordinate = annotation.coordinate;
                        [UIView animateWithDuration:0.3 animations:^{
                            annotation.coordinate = annotation.clusterAnnotation.coordinate;
                        } completion:^(BOOL finished) {
                            annotation.coordinate = actualCoordinate;
                            [self.mapView removeAnnotation:annotation];
                        }];
                    }
                }
            }
            gridMapRect.origin.x += gridSize;
        }
        gridMapRect.origin.y += gridSize;
    }
}

- (id<MKAnnotation>)annotationInGrid:(MKMapRect)gridMapRect usingAnnotations:(NSSet *)annotations {
    NSSet *visibleAnnotationsInBucket = [self.mapView annotationsInMapRect:gridMapRect];
    NSSet *annotationsForGridSet = [annotations objectsPassingTest:^BOOL(id obj, BOOL *stop) {
        BOOL returnValue = ([visibleAnnotationsInBucket containsObject:obj]);
        if (returnValue) {
            *stop = YES;
        }
        return returnValue;
    }];

    if (annotationsForGridSet.count != 0) {
        return [annotationsForGridSet anyObject];
    }
    MKMapPoint centerMapPoint = MKMapPointMake(MKMapRectGetMinX(gridMapRect), MKMapRectGetMidY(gridMapRect));
    NSArray *sortedAnnotations = [[annotations allObjects] sortedArrayUsingComparator:^(id obj1, id obj2) {
        MKMapPoint mapPoint1 = MKMapPointForCoordinate(((id<MKAnnotation>)obj1).coordinate);
        MKMapPoint mapPoint2 = MKMapPointForCoordinate(((id<MKAnnotation>)obj2).coordinate);

        CLLocationDistance distance1 = MKMetersBetweenMapPoints(mapPoint1, centerMapPoint);
        CLLocationDistance distance2 = MKMetersBetweenMapPoints(mapPoint2, centerMapPoint);

        if (distance1 < distance2) {
            return NSOrderedAscending;
        }
        else if (distance1 > distance2) {
            return NSOrderedDescending;
        }
        return NSOrderedSame;
    }];
    return [sortedAnnotations objectAtIndex:0];
} 

В одном из видеороликов Apple, посвященных WWDC 2011, показано, как именно это сделать. Перейдите на страницу https://developer.apple.com/videos/wwdc/2011/. (должен быть зарегистрированный разработчик) и перейдите к видео под названием «Географическая визуализация информации с помощью MapKit». Основная идея состоит в том, чтобы использовать представление карты за пределами экрана для хранения всех ваших аннотаций и копировать их в представление карты на экране по мере необходимости, убедившись, что вы не пытаетесь показать слишком много одновременно. Он даже делает отличную анимацию с аннотациями при масштабировании.