IP address are used to locate your machine over the network. It is a number in range 0.0.0.0 to 255.255.255.255

Range of IP addresses are distributed across the geographical region. For example. 117.195.105.53 belongs to Asia pacific region/India/Pune.

When web server receives the request from IP address assigned to you by internet service provider, they can locate your IP address location.

This is how all online analytics or web traffic monitoring systems like Google analytics or Feedjit monitors visitors activity over the web.

You might have seen Feedjit widget on many site like mine one. It gives you idea of who is visiting your site and from which region of the country.

When Brower sends a request to server, it also sends cookies associated with that request and other information like

1. Name of browser.

2. Operating system and version.

3. IP address (IP assigned to you by ISP-Internet service provider.)

Get complete list http://www.w3schools.com/asp/showasp.asp?filename=demo_server