Don't Understand Effect of Calendar Tech in Civ IV

[ArthurWalden]

The Civilopedia (and all other game info) in Civ IV says the the Calendar tech centers the world map. I'm just starting out in the game and I don't understand what this means. I also cannot find anything in the game or elsewhere explaining it. Could someone please tell me what "centering the world map" means?

Thanks.

 

[Fippy]

You can see on the mini map where you really are (globally), while before it's limited to your scouted area.