do you have permission to load test Google Maps?
I strongly suspect NOT
I would cease and desist, if you don't Google may have serious issues with you (attempted DDOS - anyone?)
checking whether the results of a 3rd party request are correct or not are rarely in scope for performance testing
functional testing should have covered this to the point that your application is sending the correct requests to Google and from that point on you really just have to assume that Google maps just works, as if it doesn't (or if it performs badly) do you have an agreement whereby they'll fix it for you
again I strongly suspect NOT
concentrate on what you have control over, ie your application, you infrastructure, NOT someone elses that you have no control over