You can add an address field and put the coordinates into the Street entry using the xxx.xxxx, (-) xxx.xxxx decimal format with NOTHING else in the contact and it will look it up properly from OSX (Mac) Address book when you LEFT click on the address title (home, work, custom, etc) and select "Map this Address".
Unfortunately, when this is synced to iOS mobile devices, they add the default country name your address book is set for, which means when you select the GPS coordinates, it goes to Maps and shows the wrong location.
Within Maps, however, you can then delete the country (which fouls it up, even if it is the correct country) and the coordinates will show you the correct location. I have not found a way to delete the country default entry in iOS.
After much searching, my conclusion is that iOS needs an update to allow for a blank country code or a field addition specifically for GPS coordinates.