Activate the following cheats by entering the corresponding passwords. Note: The map passwords will unlock full city maps that are rated "excellent". They are accessible only after a time period is selected in Free mode, and a city map is chosen:

CHEAT FUNCTION - CHEAT CODE
99,999,999 money - "MONEYBAGS"
American Prosperity Age map - "NEWWORLD"
Asia Age map - "FEUDAL"
Asia Age II map - "SAMURAI"
Dawn Of Civilization map - "ANCIENT"
Global Warming Age map - "MODERN"
Post-Global Warming map - "BEYOND"
Renaissance map - "HEREANDNOW"
Renaissance II map - "REBIRTH"

To get a higher population in Challenge mode, first save the game and select the "Quit Game" button. Choose "Yes" and select the "Challenge" tab, then load your game. Usually your population will increase dramatically (depending on the era), then it may decrease somewhat. Note: Sometimes your population will go down a bit before going up a lot.