ortega said:see this, using iPhoto, aperture can do it too
To copy the location of one photo to other photos:
You can copy the location of one photo to another photo or photos.
[*] Select a photo that has the location assigned to it that you want to copy, and then choose Edit > Copy.
[*] Select one or more photos that you want to assign the same location to, and choose Edit > Paste Location.
The location is added to the photos, which you can then view using Places.
Thanks Ortega. I have done this before. It is not a bad solution but it doesn't actually edit the EXIF so it works as long as the photos stay in iPhoto. Once exported, they will be gone again. I think there is software to edit the EXIF but all require additional work. The advantage of buying a GPS unit of course is that all will be auto. Maybe for lazy people like me.