A city is a place which has 10 people who are always there to make a minyan.

If reading the megila will come out on Shabbos, we read on an earlier day. However, the bringing of korbanos for the families who brought wood for the Bais Hamikdash, if the day came out on Shabbos, we wait until Sunday. The same is true of Tisha Bav, the korban chagiga [korban shelamim brought by private people on Yom Tov], and the mitzvah of Hakhail. If they come out on Shabbos, we wait until Sunday to do them.

Even though we can read the megila earlier, we are permitted to say eulogies and fast on that day. The mitzvah of giving to the poor on Purim also is done earlier.

R’ Yehuda says the law stating that a village can read the megila earlier is only in places where they anyway go into the city on Monday and Thursday.

Megila 1 :4

If you read the megila on Purim in Adar 1 and then they added another Adar, you must read the megila in the 2^nd Adar.

There is no difference between the 1^st Adar and the 2^nd except for the reading of the megila and giving to the poor, matanos levyonim, which is done in the second Adar.