cities, city's

Cities or cities is the plural ( more than one ) of "city", meaning a large town or metropolis--
They plan to visit all of the great cities of Europe.
People in the cities usually pay higher rents and higher taxes.

City's or city's ( rhymes with cities ) is the possessive ( belonging to ) form of "city", meaning a large town or metropolis--
Our city's mayor will be making a speech this afternoon.
The city's parade attracts visitors from all over.

City's or city's may also be a contraction ( short, informal form ) of "city is"--
The city's having a festival this weekend.
The city's only an hour's drive away.

Now that you know that, you can say--
"Our city's taxes are higher than taxes in other cities."
"This city's taxes are higher than the other city's taxes."
"The city's going to raise taxes. They'll be as high as that city's taxes."

Note--when a word ends in "y", the plural is made by dropping the "y" and adding "ies"--
One city or two cities.
One party or two parties.
One factory or two factories.
One lady or two ladies.
The possessive form of a word that ends in "y" is made the same way as other possessives--by adding an apostrophe and an "s" ( 's ) --
The city's buildings are tall.
The party's chairman is going to visit.
The factory's whistle is blowing.
The lady's hat is pretty.
Words that end in "y" may be made into a contraction ( short informal form ) with "is", by adding an apostrophe and an "s" ( 's ), the same spelling as the possessive form--
The city's going to have a parade.
The party's over.
The factory's going to close down.
The lady's wearing a pretty hat.