First, see this post: https://discussions.apple.com/thread/5479959?answerId=23519703022#23519703022
If that's not it, then it sounds like the Maps application is not able to contact the server that it gets map data from. First, sounds obvious, but make sure that your Mac can browse the Internet normally. Then, make sure that If you are running any 3rd party firewalls or anti-virus software you may want to try disabling them. If you are using a proxy, then try using a direct Internet connection instead.
One useful test might be to make sure that your iPhone is joined to the same WiFi as your Mac (and therefore not using 3G wireless connectivity), and then see if you can view a map area that you have never viewed before (try a different part of the courtry so it's not cached data).
Hopefully these help solve or at least troubleshoot your Maps issue.