Question

When I debug code below, I see that span is changed by mapkit from what I have provided. span2 contains different numbers from what was provided. Why is this happening?

- (void) viewDidLoad
{
    [super viewDidLoad];

    CLLocationCoordinate2D loc;
    loc.latitude = self.atm.lat;
    loc.longitude = self.atm.lon;

    MKCoordinateSpan span1 = MKCoordinateSpanMake(0.05f, 0.05f);
    self.mapView.region = MKCoordinateRegionMake(loc, span1);
    // at this point numbers are not 0.05 anymore
    MKCoordinateSpan span2 = self.mapView.region.span;
// ... more code
}

Answer 1

Note that latitude and longitude change differently so square MapView will actually display region with different span values for its coordinates. This is likely to cause your mapview region to have span (slightly?) different from what you set.

In reference for MKMapView’s region property there’s somewhat relevant phrase:

Changing only the center coordinate of the region can still
cause the span to change implicitly.
This is due to the fact that the
distances represented by a span change
at different latitudes and longitudes
and the map view may need to adjust
the span to account for the new
location.