I used to use some software called Openwebscope to create the graphs but this used to involve downloading large log files from the server and then running them through the software to analyse the data.
In recent years things have progressed a lot and you can now look at the data via a web page based system.
Below is a screen grab of SmartStats Enterprise running on my web host.
My website has been online since 2001 but stats like these were not as easy to create as they are now.
Statistical web site visitor traffic for derbyphotos.co.uk over last three years :