How about this?
#5 The mayor announced new city planning.
Grammatically, it is fine. However, it would probably not be used in "the real world" because it is so vague, and so doesn't really say anything.
I did some searching on the web, and came up with a number of example sentences which are better, as they are more specific. I tried to simplify them to make them easier for high school students to learn from. You are welcome to use any of these if you care to.
The mayor announced a plan to build a tunnel beneath the city in order to improve the traffic situation.
The mayor announced a plan to move city hall.
The mayor announced a plan to reduce the number of people injured in car accidents.
The mayor announced a plan to provide summer employment for 5000 young people.
The mayor announced a plan to clean up the downtown area.
The mayor announced a plan to provide housing for the homeless.
If you really want to use the phrase "city planning", consider these:
The department of city planning issued new policies to protect the environment.
The city planning division has worked hard to preserve historical buildings.
Tom works in the city planning office.