What is the difference between watchdog Location and watchdog Referrer in dblog messages
The 'Location' is the URL a user/process was visiting when the watchdog entry was invoked.

The 'Referrer' is the URL that referred the user to the 'Location' URL.

So if a person goes directly from a link on http://www.google.com to http://yoursite.com/, and visiting that URL on your site generates a watchdog record, the 'Location' will be '/', and the 'Referrer' will be 'http://www.google.com'.