Check whether zoom level changed

Question

I'm using MapKit on iPhone. How can I know when the user changes the zoom level (zoom in\out the map)?

I've tried to use mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated; but that's called even when the map is only dragged. Unfortunately, when the map is dragged the mapView.region.span changes as well...

Help?

10x

Answer 1

Much more simpler answer:

The easiest way to get an Integer of the current zoom level, is by using the MapView function: regionDidChangeAnimated. This function recognizes every change in zoom and will give you the basis for the calculation of the zoom factor.

Just insert this function into your MapView class (works for Swift 3.0):

var mapView: MKMapView! = nil

...

func mapView(_ mapView: MKMapView, regionDidChangeAnimated animated: Bool) {
    let zoomWidth = mapView.visibleMapRect.size.width
    let zoomFactor = Int(log2(zoomWidth)) - 9
    print("...REGION DID CHANGE: ZOOM FACTOR \(zoomFactor)")
}

And you will get a zoomFactor value out of it, where 0 is the most near point you can zoom into the map and every higher value is a far far away zoom... :-)

Answer 2

you can listen to the mapView:regionDidChangeAnimated: method. However, this doesn't tell you if the zoom level changed, just if the map was animated.

You will also need to listen to the region property of the map view. This contains the latitudeDelta and the longitudeDelta values which can be used to calculate if the zoom level has changed.

i.e. in the .h file

@class MyMapViewController {
    ...
    MKCoordinateRegion mapRegion;
    }
@end

and in your .m file

- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated {
    mapRegion = mapView.region;
}

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated {
    newRegion = mapView.region;

    if (mapRegion.span.latitudeDelta != newRegion.span.latitudeDelta ||
        mapRegion.span.longitudeDelta != newRegion.span.longitudeDelta)
        NSLog(@"The zoom has changed");
}

This should detect if the map zoom has changed.

however, you should wach out for the zoom changing because the earth is curved :( If the map is scrolled the latitudeDelta and longitudeDelta will change slightly just because of the shape of the Earth, not because the user has zoomed. You might have to detect a large change in the deltas and ignore slight changes.

Hope that helps.

Answer 3

Count zoom scale in MKMapView - Swift solution

I created following extension for MKMapView, so you can get a scale of zoom on map. The solution is similar as presented above but in Swift.

There is also additional function scaleWithPrecision(_:Int64) for rounding that scale what allow to filter out f.ex. little zoom changes on MapView

extension MKMapView {

    var scale: Double {

        return self.scaleWithPrecision(1)
    }

    func scaleWithPrecision(precision: Int64) -> Double {

        let mapBoundsWidth = Double(self.bounds.size.width)
        let mapRectWidth:Double = self.visibleMapRect.size.width

        let scale: Double = round(Double(precision)*mapBoundsWidth/mapRectWidth)/Double(precision)

        return scale
    }
}

Answer 4

I found this very helpful and developed the following code based on these answers.

- (void)mapView:(MKMapView *)mapView regionWillChangeAnimated:(BOOL)animated 
{
   mapRegion = self.mapView.region;
}


-(void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated{

MKCoordinateRegion newRegion = self.mapView.region;

NSInteger zFactor;
if ((mapRegion.span.latitudeDelta/newRegion.span.latitudeDelta) > 1.5){
    NSLog(@"Zoom in changed");
    zFactor = 20;
    CustomPlacemark *aO; 
    MKAnnotationView *aV; 
    for (aO in self.mapView.annotations) {
        aV = [[self mapView] viewForAnnotation:aO];
        aV.frame = CGRectMake(aV.frame.origin.x, aV.frame.origin.y, aV.frame.size.width+zFactor, aV.frame.size.height+zFactor);
        [[[self mapView] viewForAnnotation:aO] setFrame:aV.frame];
    }
}
if ((mapRegion.span.latitudeDelta/newRegion.span.latitudeDelta) < 0.75){
    NSLog(@"Zoom out");
    zFactor = -20;
    CustomPlacemark *aO; 
    MKAnnotationView *aV; 
    for (aO in self.mapView.annotations) {
        aV = [[self mapView] viewForAnnotation:aO];
        aV.frame = CGRectMake(aV.frame.origin.x, aV.frame.origin.y, aV.frame.size.width+zFactor, aV.frame.size.height+zFactor);
        [[[self mapView] viewForAnnotation:aO] setFrame:aV.frame];
    }
  }
}

Answer 5

I have the following MKMapView category in which I include a method for quickly getting the current zoom level for the map:

@implementation MKMapView (ZoomLevel)

- (NSUInteger) zoomLevel {
    MKCoordinateRegion region = self.region;

    double centerPixelX = [MKMapView longitudeToPixelSpaceX: region.center.longitude];
    double topLeftPixelX = [MKMapView longitudeToPixelSpaceX: region.center.longitude - region.span.longitudeDelta / 2];

    double scaledMapWidth = (centerPixelX - topLeftPixelX) * 2;
    CGSize mapSizeInPixels = self.bounds.size;
    double zoomScale = scaledMapWidth / mapSizeInPixels.width;
    double zoomExponent = log(zoomScale) / log(2);
    double zoomLevel = 21 - zoomExponent;

    return zoomLevel;
}

@end

To obtain the zoom level, you can call the following in your delegates and determine if the zoom level has changed:

- (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated {
    NSUInteger zoomLevel = [mapView zoomLevel];
}

Answer 6

You could save a latitude delta, then when regionDidChangeAnimated: is called, check to see if the new latitude delta is different. I think the latitude delta stays constant as long as the map isn't zoomed.