This is an interface addon for World of Warcraft: Classic which records details about characters currently online in your realms faction at the time of the polling. This is done with liberal use of the in-game /who command. The information is then stored in the CensusPlusClassic.lua in your account's SavedVariables folder, which can be uploaded to the aggregator website Wow Classic Population. This site sorts all uploaded information and displays it in chart and graph form.
These instructions will explain you how to install the addon and how you can participate in collecting census data.
Donwload the latest version of the addon: CensusPlusClassic.zip
C:\Program Files\World of Warcraft\_classic_\Interface\AddOns
C:\Program Files\World of Warcraft\_classic_\WTF\Account\ACCOUNT_NAME\SavedVariables\
and find the CensusPlusClassic.luaCensusPlusClassic.lua
on WowClassicpopulation.com