Code for those Apps where we need to update user's current location in regular interval of time even if app is in background state.

In Appdelegate.h write this code:-

@property (nonatomic,strong) UIBackgroundTaskIdentifier *bgTask;

In AppDelegate.m write this code:-

-(void) applicationDidEnterBackground:(UIApplication *) application
{
    // First tracking and check that you are on a device that supports this feature.
    // Also you will want to see if location services are enabled at all.

       [locationManager startMonitoringSignificantLocationChanges];
}

-(void) applicationDidBecomeActive:(UIApplication *) application
{
       [locationManager stopMonitoringSignificantLocationChanges];
       [locationManager startUpdatingLocation];
}

-(void) locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    BOOL isInBackground = NO;
    if ([UIApplication sharedApplication].applicationState == UIApplicationStateBackground)
    {
        isInBackground = YES;
    }

    // Handle location updates as normal, code omitted.
    if (isInBackground)
    {
        [self sendBackgroundLocationToServer:newLocation];
    }
    else
    {
        // ...
    }
}

-(void) sendBackgroundLocationToServer:(CLLocation *)location
{
    // REMEMBER. We are running in the background if this is being executed.
    // We can't assume normal network access.
    // bgTask is defined as an instance variable of type UIBackgroundTaskIdentifier

    // Note that the expiration handler block simply ends the task. It is important that we always
    // end tasks that we have started.

    bgTask = [[UIApplication sharedApplication]
               beginBackgroundTaskWithExpirationHandler:
               ^{
                   [[UIApplication sharedApplication} endBackgroundTask:bgTask];
                }];

    // ANY CODE WE PUT HERE IS OUR BACKGROUND TASK

    // For example, I can do a series of SYNCHRONOUS network methods (we're in the background, there is
    // no UI to block so synchronous is the correct approach here).

    // ...

    // AFTER ALL THE UPDATES, close the task

    if (bgTask != UIBackgroundTaskInvalid)
    {
        [[UIApplication sharedApplication} endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }
}

Happy Coding :)