My problem was how to set the gps location of my app when running in the iOS simulator
The home screen in my app displays sunrise and sunset times based on gps location and I wanted a screen shot with sensible values - I'm in the UK and the sunrise times were showing UK times for American sunrise and sunset.
As it is on the launch screen one solution, going to Debug -> Simulate Location, is too late for me.
Took me a while to work out and I wasn't finding the answer when I searched here (maybe not asking the question the right way . So I'm going to answer my own question below in the hope it stops someone else wasting their time
add a .GPX file to your project, and use XCode's location simulation feature. You can set up the location simulation as part of your scheme, so it's in place at launch time. Look under Edit Scheme, select "Run" at left, go to Options tab.