iPhone: How to draw line between two points on MapKit?

First make your view controller implement the MKMapViewDelegate protocol and declare the properties you will need:

@property (nonatomic, retain) MKMapView *mapView; //this is your map view
@property (nonatomic, retain) MKPolyline *routeLine; //your line
@property (nonatomic, retain) MKPolylineView *routeLineView; //overlay view

then in viewDidLoad (for example, or wherever you initialize)

//initialize your map view and add it to your view hierarchy - **set its delegate to self***
CLLocationCoordinate2D coordinateArray[2];
coordinateArray[0] = CLLocationCoordinate2DMake(lat1, lon1); 
coordinateArray[1] = CLLocationCoordinate2DMake(lat2, lon2);


self.routeLine = [MKPolyline polylineWithCoordinates:coordinateArray count:2];
[self.mapView setVisibleMapRect:[self.routeLine boundingMapRect]]; //If you want the route to be visible

[self.mapView addOverlay:self.routeLine];

then implement the MKMapViewDelegate‘s method -(MKOverlayView *)mapView:viewForOverlay:

-(MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id<MKOverlay>)overlay
{
    if(overlay == self.routeLine)
    {
        if(nil == self.routeLineView)
        {
            self.routeLineView = [[[MKPolylineView alloc] initWithPolyline:self.routeLine] autorelease];
            self.routeLineView.fillColor = [UIColor redColor];
            self.routeLineView.strokeColor = [UIColor redColor];
            self.routeLineView.lineWidth = 5;

        }

        return self.routeLineView;
    }

    return nil;
}

You can adjust the code to fit your need, but it’s pretty much straight forward for 2 or more points.