As I was uploading my memory maps at Flickr (based on Matt Haughey‘s initial post), I realized the four that I uploaded had something in common, besides just places that I have lived.
The trait they have in common is public knowledge and a simple item, one we use all the time. There is one exception. The trait for the area I lived in Southern California has recently changed but is still the same further south of Oceanside.
For the first person who figures this one out, I will either pay to upgrade your Flickr account to Pro, or buy you one of the O’Reilly Hacks books of your choice. I have two email addresses listed on my Flickr account page or leave your answer in the comments (they’re moderated).
Good luck. Post comments if you have further questions. I’m also adding hints to the captions so be sure to read those on each of the photos.

Comments (7)
Area codes:
Minneapolis 612
Oceanside 619 (formerly)
Carbondale 618
Smyrna 615
You are correct, sir! Name your prize. Flickr Pro or your choice of an O’Reilly Hacks book.
Flickr Pro, please!
Thanks! What a terrific contest!
All right. You should be covered for the next year as a Flickr Pro user. Enjoy and take lots of pictures.
FIX YOUR FUCKING FRAMES!
Ha, I thought it was “baseball diamonds” silly me! :)
What frames need fixing, Mr. Tolar?