There is a pie chart of favorite maps (past week) on the page

https://www.gametracker.com/server_info/zm.net4all.su:27015/

but I would like to see a more detailed statistics (not just top 5 maps) and the actual description of what do the numbers represent. Are those numbers based on the overall time they last on the server or just on the number of times they are played. Is it possible?

The historical map graph is based on the number of times a map is played. That should relatively closely match the amount of time played per map, for the vast majority of servers.

If you have a proposal on how to improve the map section, feel free to create an idea thread in:

http://www.gametracker.com/forums/forum.php?site=1&category=164145