Sometimes, in maps, you might need to display entire-world-view. Example, in case of no location found, zoom out to the world view. Following code-snip would help you to achieve the same.

zoomOutToWorldView.m

// this code will help you to zoom out to world-view

// step.1 create co-ordianate-span as follows
MKCoordinateSpan span = {.latitudeDelta = 180, .longitudeDelta = 360};

// step.2 crate region as follows
MKCoordinateRegion region = MKCoordinateRegionMake(CLLocationCoordinate2DMake(0.0000f, 0.0000f), span);

// step.3 zoom using region to map as follows
[self.mapView setRegion:region animated:YES];

// ------------------------------------------------------------

//achieves the same effect you are going after.. MKMapRectWorld <- available since iOS 4.0
[self.mapView setVisibleMapRect:MKMapRectWorld animated:YES];