Comments on: Set the Zoom Level of an MKMapView

By: Robert Altman

Robert Altman — Wed, 09 Nov 2011 23:57:14 +0000

I believe there is quite a significant error in the original code (and all variations). The line

NSInteger zoomExponent = 20 – zoomLevel;

should actually be:

NSInteger zoomExponent = 21 – zoomLevel;

I combined the setCenterCoordinate:zoomLevel:animated: code with the getZoomLevel function (see walty’s post)and created / connected two buttons (Zoom+ and Zoom-). It’s fairly simple code:

[mapView setCenterCoordinate:mapView.centerCoordinate zoomLevel:mapZoomLevel+1 ...];

and

[mapView setCenterCoordinate:mapView.centerCoordinate zoomLevel:mapZoomLevel-1 ...];

The result was zoom buttons which jump up 2 increments (Zoom+) or 0 (Zoom -).

The value 268435456 is actually quite significant: it is the number of pixels (horizontal or vertical) at zoom level 20. Tiles are always 256 x 256 pixels. The value 268435456 == 256 * 2 ^20; in other words, at zoom level 20, there are 1048576 (or 2 ^ 20) tiles, each with 256 (2 ^ pixels.

I’m very confident in the zoomLevel calculations; I base-lined the equation by measuring MapKit tiling at its minimum magnification. At minimum zoom, in a full-screen iPad view, MapKit shows 16 tiles, which correlates to zoom level 2.

If you try using the erroneous code, and setting your zoom level to 2 (which should show 16 tiles), you will actually have a map at zoom level 3 (containing 64 files).

Thanks for a great writeup – it’s been hard validating all of the related map math, and this (and your other mapping explanation) saved me a bunch of time in doing so.

By: PostaL

PostaL — Fri, 09 Sep 2011 08:11:22 +0000

Voila, not viola

10x for the nice code

By: Jimmy Theis

Jimmy Theis — Sun, 04 Sep 2011 19:42:30 +0000

Hi Troy,

I’m not sure if I missed it, but there doesn’t seem to be a clear set of distribution terms with your code here. Your blog has a general copyright, but your language makes this code sound like it’s free for anyone to use. Is your work here Public Domain? Released under a specific Open Source License?

Thanks

By: Nik

Nik — Mon, 01 Aug 2011 03:47:53 +0000

I found it much simpler to set the visibleRect than to set the region of an MKMapView (and more accurate results too, when using a specific zoomScale, as opposed to a zoomLevel.

- (MKMapRect)mapRectWithCentreCoordinate:(CLLocationCoordinate2D)centreCoordinate zoomScale:(double)zoomScale
{
MKMapPoint centrePoint = MKMapPointForCoordinate(centreCoordinate);
double scaledWidth = self.bounds.size.width / zoomScale;
double scaledHeight = self.bounds.size.height / zoomScale;

return MKMapRectMake(centrePoint.x – (scaledWidth / 2),
centrePoint.y – (scaledHeight / 2),
scaledWidth,
scaledHeight);
}

- (void)setCentreCoordinate:(CLLocationCoordinate2D)centreCoordinate zoomScale:(double)zoomScale animated:(BOOL)animated
{
[self setVisibleMapRect:[self mapRectWithCentreCoordinate:centreCoordinate zoomScale:zoomScale] animated:animated];
}

and then if you want it to work for zoomLevel, as well as for zoomScale, you can reuse the same code simply by adding the following (untested):

- (void)setCentreCoordinate:(CLLocationCoordinate2D)centreCoordinate zoomLevel:(NSUInteger)zoomLevel animated:(BOOL)animated
{
// clamp large numbers to 28
zoomLevel = MIN(zoomLevel, 28);

[self setCentreCoordinate:centreCoordinate zoomScale:[self zoomScaleForZoomLevel:zoomLevel] animated:animated];
}

By: Raks

Raks — Mon, 11 Jul 2011 22:05:53 +0000

Awsome code but somehow I am receiving following error “implicit-conversion-shortens-64-bit-to-32-bit” at code “return round(MERCATOR_OFFSET – MERCATOR_RADIUS * logf((1 + sinf(latitude * M_PI / 180.0)) / (1 – sinf(latitude * M_PI / 180.0))) / 2.0)”…any idea why ?

Thanks,

By: Kevin Scott

Kevin Scott — Thu, 30 Jun 2011 20:23:55 +0000

AWESOME! SO AWESOME! Thanks Thanks Thanks!!!

This code rocks my socks off. Also props to Walty for the getZoomLevel as well.

By: Mega Lee

Mega Lee — Mon, 27 Jun 2011 03:55:13 +0000

It is so powerful ! Thank you !

Where is an example to download !?

When I use this ,could it pass the AppStore!?

By: Marco Faustinelli

Marco Faustinelli — Mon, 30 May 2011 10:48:04 +0000

I enjoyed your post very much.
However I wonder how much room there is for approximation: my app is based on Google Static Maps, it will use zoomlevels 13-18 and it will always be used with geo-location in central-european countries. I’ve been looking for a simple table providing me with the relation between pixelDelta and latLongDelta given zoomLevel, but I couldn’t find it. My intention is to implement your routines once to calculate those relations and feed them to my app, publishing a blog page in the process.
What is your take with regards to the magnitude of error that this process will entail? Thanks in advance, and again thanks a lot for publishing this page

By: John D Pope

John D Pope — Wed, 27 Apr 2011 00:40:46 +0000

Merged zoomLevel changes and Adam Cohen-Rose code here https://github.com/jdp-global/MKMapViewZoom

By: Ashok

Ashok — Sun, 03 Apr 2011 02:28:28 +0000

Wow, thanks for this! I was struggling trying to do this myself with the setRegion: method and trying to set the latitudeDelta and longitudeDelta and wasn’t getting anywhere.

This worked on the first try!