I have been working on some mapping stuff recently in the iOS space and have built myself up a few bits and pieces which make up some good categories on the MKMapView. They are attached below:

@interface MKMapView (Extensions)

/**
@brief Will return all annotations on the map except for the users.
*/
-(NSArray*)annotationsWithoutUserLocation;

/**
@brief Returns YES if the specified region is "null".
*/
+ (BOOL) isMKCoordinateRegionNull: (MKCoordinateRegion) region;

/**
@brief Returns YES if the specified region is "null" or empty.
*/
+ (BOOL) isMKCoordinateRegionEmpty: (MKCoordinateRegion) region;

/**
@brief Returns a debug description string for the region.
*/
+ (NSString*) MKCoordinateRegionDebugDescription: (MKCoordinateRegion) region;

/**
@brief This method will fit and zoom all the annotations onto the map
*/
-(void) zoomToFitAnnotations;

/**
@brief This method will fit and zoom all the annotations on the map except the user one
*/
-(void) zoomToFitAnnotationsWithoutUserLocation;

@end

#import "MKMapView+Extensions.h"

@implementation MKMapView (Extensions)
-(NSArray*)annotationsWithoutUserLocation
{
// remove the user location which also is considered an annotation
NSMutableArray *annotations = [NSMutableArray arrayWithArray:self.annotations];
if ( self.userLocation )
[annotations removeObject:self.userLocation];

return annotations;
}

+ (BOOL) isMKCoordinateRegionNull: (MKCoordinateRegion) region;
{
return isinf(region.center.latitude) || isinf(region.center.longitude);
}

+ (BOOL) isMKCoordinateRegionEmpty: (MKCoordinateRegion) region
{
return [MKMapView isMKCoordinateRegionNull: region] || (region.span.latitudeDelta == 0.0 && region.span.longitudeDelta == 0.0);
}

+ (NSString*) MKCoordinateRegionDebugDescription: (MKCoordinateRegion) region
{
return [NSString stringWithFormat:@"{center: {%f,%f}, span: {%f,%f}}",
region.center.latitude,
region.center.longitude,
region.span.latitudeDelta,
region.span.longitudeDelta];
}

-(void) zoomToFitAnnotations {
MKMapRect zoomRect = MKMapRectNull;
for (id annotation in self.annotations) {
MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0, 0);
if (MKMapRectIsNull(zoomRect)) {
zoomRect = pointRect;
} else {
zoomRect = MKMapRectUnion(zoomRect, pointRect);
}
}
[self setVisibleMapRect:zoomRect animated:YES];
}

-(void) zoomToFitAnnotationsWithoutUserLocation {
MKMapRect zoomRect = MKMapRectNull;
for (id annotation in self.annotationsWithoutUserLocation) {
MKMapPoint annotationPoint = MKMapPointForCoordinate(annotation.coordinate);
MKMapRect pointRect = MKMapRectMake(annotationPoint.x, annotationPoint.y, 0, 0);
if (MKMapRectIsNull(zoomRect)) {
zoomRect = pointRect;
} else {
zoomRect = MKMapRectUnion(zoomRect, pointRect);
}
}
[self setVisibleMapRect:zoomRect animated:YES];
}

- (void) zoomToAnnotation:(id )annotation {
MKCoordinateSpan span = {0.027, 0.027};
MKCoordinateRegion region = {[annotation coordinate], span};
[self setRegion:region animated:YES];
}

- (MKMapRect) getMapRectUsingAnnotations:(NSArray*)theAnnotations {
MKMapPoint points[[theAnnotations count]];

for (int i = 0; i <; [theAnnotations count]; i++) {
id annotation = [theAnnotations objectAtIndex:i];
points[i] = MKMapPointForCoordinate(annotation.coordinate);
}

MKPolygon *poly = [MKPolygon polygonWithPoints:points count:[theAnnotations count]];

return [poly boundingMapRect];
}

- (void) addMapAnnotationToMapView:(id )annotation {
if ([self.annotations count] == 1) {
// If there is only one annotation then zoom into it.
[self zoomToAnnotation:annotation];
} else {
// If there are several, then the default behaviour is to show all of them
//
MKCoordinateRegion region = MKCoordinateRegionForMapRect([self getMapRectUsingAnnotations:self.annotations]);

if (region.span.latitudeDelta <; 0.027) {
region.span.latitudeDelta = 0.027;
}

if (region.span.longitudeDelta <; 0.027) {
region.span.longitudeDelta = 0.027;
}
[self setRegion:region];
}

[self addAnnotation:annotation];
[self selectAnnotation:annotation animated:YES];
}

@end