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After updating to iOS 6 I have noticed sever performance decreases when panning or zooming a MKMapView with multiple overlays. An app I created has approximately 600 polygon overlays of various colours, and ran lag-free (even on older iOS devices) on iOS 5, now runs extremely laggily (when zooming & panning) on iOS 6, even on the latest devices.

My hunch is that this is due to the fact the device has to actually dynamically create the map (since its vector based) rather than just display tiles onscreen.

Has anyone got any ideas to reduce the lag experienced when panning or zooming the map?

Some extra info, this low frame rate also occurs whilst zooming or panning areas where the overlays are not displayed on screen at all, so it is not to do with the creation of the overlays as they come onscreen.

Tom H
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  • Did you profile the performance issue with instruments? – Felix Oct 16 '12 at 16:55
  • How would I best test that? What instrument should I use? – Tom H Oct 16 '12 at 19:30
  • use time profiler (if the problem is cpu bound) - it will show you where the most time is spend in your code – Felix Oct 16 '12 at 20:46
  • Can you share your drawing code? Mapkit calls the drawMapRect: method and passes a mapRect. This mapRect may or may not encompass your overlay. Its your job to only draw the part of your overlay that overlaps the drawrect. A lot of code on the web draws the entire overlay for each drawrect. – Bill Johnson Mar 16 '13 at 13:01

2 Answers2

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You can try combining all of your overlays into a single one. This can dramatically boost performance.

The idea is to create an overlay with a bounding box that encompasses all of your polygons. This way your mapView: viewForOverlay will always be called. Create a property for your overlay that holds all of your polygons. Then in the drawMapRect: method of your overlay view, test all of your polygons for intersection with mapRect and draw them if necessary. This is important since you don't want to be drawing polygons that are off screen.

This strategy is based on Apple's own MapKit example projects. Check out HazardMap for an example of drawing several objects in a single MKOverlayView and check out BreadCrumb for an example of how to efficiently test polygons for intersection with your current mapRect in the drawMapRect method

Jeff Ames
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I have a minimalistic MapKit tech demo and it's lagging noticeably as I run it on an iPad 3 with iOS6. Profiling reveals that it's CPU bound, but only 0.2% is from my own code. The big culprits in my case are rendering roads, followed by rendering labels - both done by MapKit. I am showing downtown San Francisco at a 5KM scale, so there are a lot of roads and labels to render.

So the moral of the story is: iOS6 maps are SLOW. Can't tell you how this compares to iOS5 or to an iPad 2, though. But it's lagging, and I am barely doing any work of my own at all.

P.S: Open Instruments and use the Time Profiler. Make a recording + drill down to find your culprits. Then check 'hide system libraries' to find out how much of the lag is your responsibility vs MapKit's. Then optimize only as needed.

Rolf Hendriks
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