Those square metal plates on roads

I decided I was going to figure out what those square metal plates you find on roads around here are. 

As it turns out, and how they're used at least in Stark County Ohio, they are considered to be surveyor benchmarks used to mark things like the center line of roads. I was able to find a webpage that has some GIS data released that indicates where these are. The compressed file is about 5.26MB, and considering there's a lot of these surveyor benchmarks, that file size sounds about right. Only thing is, you have to use Google Earth Pro if you want something to easily and directly import that data. There appear to be tools to do it without Google Earth Pro, but with 50 MEGS of data, I'm not going to even begin.

I just wanted to know what they are. And I found out.