try this,
NSString *urlstring=[NSString stringWithFormat:@"http://maps.google.com/?saddr=%f,%f&daddr=%f,%f",sourcelocation.latitude,sourcelocation.longitude,destinationlocation.latitude,destinationlocation.longitude];
[[UIApplication sharedApplication]openURL:[NSURL URLWithString:urlstring]];
What the code do is, it will show the route between your source and destination location on google map.
If you dont have the longitude then you can do it like:-
NSString *source=@"NorthCarolina";
NSString *destination=@"SouthCarolina";
NSString *urlstring=[NSString stringWithFormat:@"http://maps.google.com/?saddr=%@&daddr=%@",source,destination];
[[UIApplication sharedApplication]openURL:[NSURL URLWithString:urlstring]];
I hope this will help you.Happy coding:)