the visitor amount for our intranet is way too high. We are approximately 6k employees, and on a monthly basis, it is showing 16k unique visitors.
The employees almost exclusively use one browser and one device (desktop), so it is not a question of toggling between different devices and browsers.
I have checked in the debugger to made sure that my Cookie-ID is the same throughout the week, and I am also marked as a returning visitor in the debugger. So it does not seem that different Cookie-IDs are being created for every day.
There are multiple reasons for this to happen, and some or all of them may affect your numbers at the same time:
Anonymous visitors can significantly inflate this number with each visit - if you have it on.
Every time a person uses a new device (or browser, or clears the browser history or Piwik PRO cookies are blocked altogether), they are counted as one visitor per device/browser etc.
Employee turnover - during any given period, there may be employees who were still with the company at the beginning of the selected date range, but are no longer with the company, as well as some new employees. In other words, the number of employees over time will always be higher than the current number due to turnover.
What would give you more accurate numbers (except for issue #3) would be to use User ID and track and use metric Users rather than Visitors. However, that would require custom tracking using a unique employee identifier, such as an email address or something similar.