The following lines of code helped me to draw a route between two Annotation point in MKMapView

Hope this will help you in your coding

CSRouteAnnotation* routeAnnotation = (CSRouteAnnotation*)self.routeView.annotation;

    // only draw our lines if we're not int he moddie of a transition and we 
    // acutally have some points to draw. 
    if(!self.hidden && nil != routeAnnotation.points && routeAnnotation.points.count > 0)
    {
        CGContextRef context = UIGraphicsGetCurrentContext(); 

        if(nil == routeAnnotation.lineColor)
            routeAnnotation.lineColor = [UIColor blueColor]; // setting the property instead of the member variable will automatically reatin it.

        CGContextSetStrokeColorWithColor(context, routeAnnotation.lineColor.CGColor);
        CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 1.0);

        // Draw them with a 2.0 stroke width so they are a bit more visible.
        CGContextSetLineWidth(context, 2.0);

        for(int idx = 0; idx < routeAnnotation.points.count; idx++)
        {
            CLLocation* location = [routeAnnotation.points objectAtIndex:idx];
            CGPoint point = [self.routeView.mapView convertCoordinate:location.coordinate toPointToView:self];



            if(idx == 0)
            {
                // move to the first point
                CGContextMoveToPoint(context, point.x, point.y);
            }
            else
            {
                CGContextAddLineToPoint(context, point.x, point.y);
            }
        }

        CGContextStrokePath(context);

Happy Coding