One problem with the code by Paul Shapiro is that it doesn t deal with when you add annotations below where the user is looking at the moment. Those annotations will float in mid-air before dropping because they are moved into the user s visible map rect.

Another is that it also drops the user location blue dot. With this code below, you handle both user location and large amounts of map annotations off-screen. I ve also added a nice bounce ;)

- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views {
    MKAnnotationView *aV; 

    for (aV in views) {

        // Don t pin drop if annotation is user location
        if ([aV.annotation isKindOfClass:[MKUserLocation class]]) {
            continue;
        }

        // Check if current annotation is inside visible map rect, else go to next one
        MKMapPoint point =  MKMapPointForCoordinate(aV.annotation.coordinate);
        if (!MKMapRectContainsPoint(self.mapView.visibleMapRect, point)) {
            continue;
        }

        CGRect endFrame = aV.frame;

        // Move annotation out of view
        aV.frame = CGRectMake(aV.frame.origin.x, aV.frame.origin.y - self.view.frame.size.height, aV.frame.size.width, aV.frame.size.height);

        // Animate drop
        [UIView animateWithDuration:0.5 delay:0.04*[views indexOfObject:aV] options:UIViewAnimationCurveLinear animations:^{

            aV.frame = endFrame;

        // Animate squash
        }completion:^(BOOL finished){
            if (finished) {
                [UIView animateWithDuration:0.05 animations:^{
                    aV.transform = CGAffineTransformMakeScale(1.0, 0.8);

                }completion:^(BOOL finished){
                    [UIView animateWithDuration:0.1 animations:^{
                        aV.transform = CGAffineTransformIdentity;
                    }];
                }];
            }
        }];
    }
}

First, you need to make your view controller implement MKMapViewDelegate if it doesn t already.

Then, implement this method:

- (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views { 
   MKAnnotationView *aV; 
   for (aV in views) {
     CGRect endFrame = aV.frame;

     aV.frame = CGRectMake(aV.frame.origin.x, aV.frame.origin.y - 230.0, aV.frame.size.width, aV.frame.size.height);

     [UIView beginAnimations:nil context:NULL];
     [UIView setAnimationDuration:0.45];
     [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
         [aV setFrame:endFrame];
     [UIView commitAnimations];

   }
}

Add your annotations to the MapView and when they are added, this delegate method will be called and will animate the pins from top to bottom as they are added.

The values for timing and positioning can be changed a little bit but I ve tweaked it to make it look best/closest to the traditional drop (as far as I ve tested). Hope this helps!

Alternatively, if you re making a MKAnnotationView subclass, you can use didMoveToSuperview to trigger the animation. The following does a drop that ends in a slight squish effect

  #define kDropCompressAmount 0.1

  @implementation MyAnnotationViewSubclass

  ...

  - (void)didMoveToSuperview {
      CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform"];
      animation.duration = 0.4;
      animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
      animation.fromValue = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(0, -400, 0)];
      animation.toValue = [NSValue valueWithCATransform3D:CATransform3DIdentity];

      CABasicAnimation *animation2 = [CABasicAnimation animationWithKeyPath:@"transform"];
      animation2.duration = 0.10;
      animation2.beginTime = animation.duration;
      animation2.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
      animation2.toValue = [NSValue valueWithCATransform3D:CATransform3DScale(CATransform3DMakeTranslation(0, self.layer.frame.size.height*kDropCompressAmount, 0), 1.0, 1.0-kDropCompressAmount, 1.0)];
      animation2.fillMode = kCAFillModeForwards;

      CABasicAnimation *animation3 = [CABasicAnimation animationWithKeyPath:@"transform"];
      animation3.duration = 0.15;
      animation3.beginTime = animation.duration+animation2.duration;
      animation3.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
      animation3.toValue = [NSValue valueWithCATransform3D:CATransform3DIdentity];
      animation3.fillMode = kCAFillModeForwards;

      CAAnimationGroup *group = [CAAnimationGroup animation];
      group.animations = [NSArray arrayWithObjects:animation, animation2, animation3, nil];
      group.duration = animation.duration+animation2.duration+animation3.duration;
      group.fillMode = kCAFillModeForwards;

      [self.layer addAnimation:group forKey:nil];
  }

For Michael Tyson s response (I can t comment everywhere yet), I propose an insertion of the following code in didMoveToSuperview for proper reuse of MKAnnotationView so it does the animation again and then imitate the sequencial addition of annotations

Play with the dividers and multipliers for different visual results...

- (void)didMoveToSuperview {
    //necessary so it doesn t add another animation when moved to superview = nil
    //and to remove the previous animations if they were not finished!
    if (!self.superview) {
        [self.layer removeAllAnimations];
        return;
    }


    float xOriginDivider = 20.;
    float pos = 0;

    UIView *mySuperview = self.superview;
    while (mySuperview && ![mySuperview isKindOfClass:[MKMapView class]])
        mySuperview = mySuperview.superview;
    if ([mySuperview isKindOfClass:[MKMapView class]]) 
        //given the position in the array
        // pos = [((MKMapView *) mySuperview).annotations indexOfObject:self.annotation];   
        // left to right sequence;
        pos = [((MKMapView *) mySuperview) convertCoordinate:self.annotation.coordinate toPointToView:mySuperview].x / xOriginDivider;

    float yOffsetMultiplier = 20.;
    float timeOffsetMultiplier = 0.05;


    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"transform"];
    animation.duration = 0.4 + timeOffsetMultiplier * pos;
    animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
    animation.fromValue = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(0, -400 - yOffsetMultiplier * pos, 0)];
    animation.toValue = [NSValue valueWithCATransform3D:CATransform3DIdentity];

    // rest of animation group...
}

I think the better option is to set animatesDrop to YES. It s a property of MKPinAnnotationView.