I don't want to broadcast my location constantly. But I would like the ability to grant permission to some of my friends and family to be able to look up my location when they need it. I'd also like a log and a notification when they look it up, so I know I'm not being stalked, and so they actually put thought into deciding whether or not it's appropriate to look up my location before doing so.

I imagine an app which doesn't send my location to a third party service on an interval. When somebody wants to look up my location, the app on their phone sends a request to some third party service over the Internet, which then pushes a request for my location to my phone. The first time the request comes in from a particular user, it asks me if I'd like to grant them this privilege permanently, temporarily, or to block it. If I grant it, then I don't need to approve future lookups but I am alerted to them happening.

[edit] The requests could also be of the style: "Let me know when you arrive at location x", instead of just "Let me know where you are now". Would be handy for meeting up at places on nights out.