We have seen several reports of this problem recently. The maps are missing in all older Aperture versions and iPhoto versions that are still using Google maps and not the new Apple maps. In Aperture 3.5.1 and later or iPhoto 9.5.1 and later the maps are working well.
One possible explanation for the problem is, that the contract between Google and Apple expired recently. But so far we have not seen any acknowledgement by Apple that there is a problem with the maps. So we do not know for sure, if it is caused by the end of the Google contract or a server problem like the problem with the print services for books.
See this discussion: https://discussions.apple.com/thread/7123544?answerId=28567942022#28567942022&ac_cid=tw123456#28567942
You may want to update to iPhoto 9.6.1 and Yosemite to get the places feature working again.
Make a full backup of your Mac before you upgrade - a Time Machne backup or bootable clone, so you can revert to your current system should any problems arise.
Apple stopped selling iPhoto, so it is a bit tricky to update. You will neither find an update on the Updates page of any App Store nor can you purchase iPhoto any longer. The update message, when you try to launch iPhoto is sending you on a wild goose chase. The only way to update is by reinstalling iPhoto, if you already own iPhoto and your purchase is associated with your AppleID at the Mac App Store
Barney-15E's user tip explains how to update to iPhoto 9.6.1 by reinstalling your purchase. Get iPhoto 9.6.1 if you didn't update before OS X 10.10.3
