Drop a nuke on a 70+ pop city ... Doh'
Granary , Aquaduct, Hospital And the Medical Lab ....
You need those buildings
Place you're citie you want to grow into grasland ...
Make extra production buildings like workshops and windmill so you can put it on default or food focus and build units or buildings faster
If you get freedom you're specialist consume less food as result you can use enginiers for good production and grow fast..