What does 'unique visitor' mean in the context of Google Analytics on Android?

I've got my android app reporting usage statistics to Google analytics, and everything seems pretty awesome, however my 'unique visitor' count is always wrong.

My account is reporting almost 30 unique visitors over the past month or so that I've been in development. The app is only installed on four devices. One of the devices is wi-fi only, an开发者_开发知识库d is not hooked up to a phone carrier or data plan.

So how is a 'unique visitor' defined? My current theory is that because I have uninstalled and installed the application on these devices a number of times, that each new install has become a 'unique' visitor, but I'd like to know if my theory is true or not before this gets launched in the app store. Is there some other reason my unique visitor count would be so high? Or possibly a common mistake I could be missing?

I have been pursuing this, trying through experimentation to find an answer.

Yesterday on Monday I had a reported 29 unique visitors from the previous week, with no activity on Saturday and Sunday. I very carefully performed four uninstall/installs and one 'refresh' (just installing/running the program without uninstalling it). I then removed the google analytics ID so that no more data could be sent. Analytics now reports that there were five visitors on Monday (in the graph that I click next to 'unique visitors') but a total of 35 Absolute Unique Visitors. Those numbers just don't add up.

I then realized that the date range in the top right hand corner was not the full range of time that my analytics account had been activive - but only a month. When I narrowed the date range to just the Monday, it accurately portrayed 5 absolute unique visitors. So my numbers were jumping around wildly as each day, the start date to my range changed.

So lessons learned:

• Installing your app results in a new unique visitor, even on the same device.
• Reported data is for the past 30 days by default. Play with the date range.
• A new installation of your app will only be acknowledged in analytics if your app sends the data. Double check as to when you are sending analytics data and if your app has had a chance to send data on each new install.

You can find the answer from Google itself:

Another important function of the mobile SDK is differentiating users. When an app launches for the first time the Google Analytics SDK generates an anonymous unique identifier for the device, similar to the way the website tracking code does. Each unique identifier is also counted in Google Analytics as a unique user. If the app gets updated to a new version, the identifier on the device remains the same. However, if the app gets uninstalled, the Google Analytics SDK deletes the identifier. If the app is then reinstalled, a new anonymous identifier is created on the device. The result is that the user will be identified as a new user, not a returning user, but no other data in your Google Analytics reports will be impacted.

and the full link here: https://support.google.com/analytics/answer/6083697?hl=en

For websites GA tracking is done by dropping cookies. If you clear the google analytics tracking cookies associated with a site and then visit that site again, GA will treat it as a new visitor.

Not sure if Android Apps use this same technology. But if it does then it seems that uninstalling the app is clearing the cookies associated with it.