Free visitor meters, like SiteMeter and Statcounter, are great for telling you who looks at your web site.
You can find out details like how they get there, how long they look, and many other useful details. One useful detail, not always completely understood, is where your readers are located.
The process of determining this is called Geolocation.
How accurate is geolocation, anyway?
Not very accurate for me. My ISP is in Santa Rosa. I'm not.
Using the IP address of your computer (or more frequently, the external or WAN address of your network), many experts claim to know where you are located.
Unfortunately, as in the example above, this shows where your ISP is located. Between you and your ISP is another network, called by the experts the "backhaul", that is transparent to IP and the Geolocation databases.
Your ISP could be in another city, county, state, or even country.
My location is no secret. How far is Martinez, from Santa Rosa?
Not anywhere within walking distance, obviously.
For a more graphic example of geolocation, see And Now, A Dose Of Paranoia For You.