What's the difference between small wordls,sandbox,realistic, etc.

I tried using the link for the wikia but it doesnt work, so I guess I have to resort to le forums. If anyone can tell me all of them and what they have in uncommon would be appreciated.

Realistic ® worlds have all of the restrictions for airports which apply in real life. Most also have a 2 airline per player and 300 airlines total limit, although Rα and Rδ do not have an airline per player limit, and can hold 500 airlines in total. See the bottom of this post for full restriction details.
Restrictions:
1.) Political: You cannot fly between countries when one or both of them has embargoed or blockaded air travel between the two.
2.) Legislative: Some airports have restrictions on how many seats your aircraft can have and how far it can fly.
3.) Aviation Law: You may only operate flights from your home country, all hubs and terminals be in your home country.

Open (O) worlds have none of these restrictions, allowing you to fly from wherever you want to wherever you want, no matter where you are based. However, the 2 airline per player and 300 airline total limits still apply.

Special (S) worlds can be divided into several categories:

The first Special Rules world (S1) has a limit of one hub and one terminal per player to provide an alternate game style which does not attract as many spammers.

The second Special Rules world (S2) has a ban on leasing, which is often used by players who desire rapid expanision, stifling growth and fostering different strategies with less competiton and less potential for gigantic spamlines.

Small (S3) worlds are just like realistic worlds, except that they have a limit of 100 airlines total and 1 airline per player.

There are 2 Sandbox (S4) worlds, down from the original 5, whose identifications ran from S4A to S4E:

The standard Sandbox world (S4B) is similar to an Open (O) world, but has some significant differences to allow players to try out new ideas.
1.) Each airline starts with $100,000,000 (instead of the usual $7,500,000).
2.) The moment an aircraft enters production, the used market is filled with cheap options which have no previous owner, unlike in other worlds.
3.) The game speed is only 5 minutes per day, causing Sandbox (S4) worlds to progress extremely fast, so you should not treat them as a real game.
4.) Trophies are not awarded for Sandbox (S4) worlds.

The second Sandbox world (S4E) is exactly the same as the standard world (S4B), but requires that a player’s account be less than 90 days old at the time of the airline’s creation, making it a good way for new players to learn the game.

Restrictions:

1.) Political: You may not operate a flight departing from or arriving in one of the below countries if the flight also departs or arrives at one of the countries listed beneath it.

Cuba:

The United States of America

Gaza Strip:

Israel
The United States of America

Indonesia:

Israel

Iran:

Israel
The United States of America

Iraq:

Israel

Israel:

Gaza Strip
Indonesia
Iran
Iraq
Malaysia
Saudi Arabia
Syria
The United Arab Emirates

Malaysia:

Israel

North Korea:

South Korea
The United States of America

Saudi Arabia:

Israel

South Korea:

North Korea

Syria:

Israel
The United States of America

The United Arab Emirates:

Israel

The United States of Anerica:

Cuba
Gaza Strip
Iran
North Korea
Syria

2.) Legislative: The following airports in the United States of America place restrictions upon departing and arriving flights:

Dallas Love Field (DAL):

All aircraft with the capacity to hold more than 56 seats are limited to serving airports located in Texas, New Mexico, Oklahoma, and Arkansas. However, aircraft with a maximum capacity of 56 seats or less have no restrictions. It is not possible to configure aircraft which could potentially hold more seats, such as the 737-800, which has a maximum of 189 seats, with 56 seats in order to avoid these restrictions.

New York LaGuardia (LGA):

Flights departing from and arriving at the airport must be less than 1500 miles in length.

Washington National (DCA):

Flights departing from and arriving at the airport must be less than 1250 miles in length.

3.) Aviation Law:

Exception 1.) European Union (Post-2000):

EU-based airlines may operate flights between countries that are part of the EU. However, you can't operate flights outside from another EU country to a non-EU country. For example, if an airline was based in the United Kingdom, they could operate flights from Paris to Oslo; however, they could not operate flights from Paris to New York. The following countries are members of the EU:

Austria
Belgium
Czech Republic
Denmark (excluding Greenland)
Estonia
Finland
France (excluding overseas departments and territories)
Germany
Greece
Hungary
Iceland
Italy
Latvia
Liechtenstein
Lithuania
Luxembourg
Malta
Netherlands
Norway
Poland
Portugal
Republic of Ireland
Slovakia
Slovenia
Spain (excluding Ceuta and Melilla)
Sweden
United Kingdom

Exception 2.) Trans-Tasman Travel Agreement (Post-1983):
Airlines based in Australia or New Zealand may treat both nations as their home country, for the purposes of domestic flights, the running hubs, and the ownership terminals. However, an airline may not operate international flights from any country except their own, though flights between Australia and New Zealand are unrestricted in origin.

NOTE: S1 and S2 do not actually prevent spamlines

There are usually not as many, in my experience. They can happen, but not on the scale of the emperor...

Realistic ® worlds have all of the restrictions for airports which apply in real life. Most also have a 2 airline per player and 300 airlines total limit, although Rα and Rδ do not have an airline per player limit, and can hold 500 airlines in total. See the bottom of this post for full restriction details.
Restrictions:
1.) Political: You cannot fly between countries when one or both of them has embargoed or blockaded air travel between the two.
2.) Legislative: Some airports have restrictions on how many seats your aircraft can have and how far it can fly.
3.) Aviation Law: You may only operate flights from your home country, all hubs and terminals be in your home country.

Open (O) worlds have none of these restrictions, allowing you to fly from wherever you want to wherever you want, no matter where you are based. However, the 2 airline per player and 300 airline total limits still apply.

Special (S) worlds can be divided into several categories:

The first Special Rules world (S1) has a limit of one hub and one terminal per player to provide an alternate game style which does not attract as many spammers.

The second Special Rules world (S2) has a ban on leasing, which is often used by players who desire rapid expanision, stifling growth and fostering different strategies with less competiton and less potential for gigantic spamlines.

Small (S3) worlds are just like realistic worlds, except that they have a limit of 100 airlines total and 1 airline per player.

There are 2 Sandbox (S4) worlds, down from the original 5, whose identifications ran from S4A to S4E:

The standard Sandbox world (S4B) is similar to an Open (O) world, but has some significant differences to allow players to try out new ideas.
1.) Each airline starts with $100,000,000 (instead of the usual $7,500,000).
2.) The moment an aircraft enters production, the used market is filled with cheap options which have no previous owner, unlike in other worlds.
3.) The game speed is only 5 minutes per day, causing Sandbox (S4) worlds to progress extremely fast, so you should not treat them as a real game.
4.) Trophies are not awarded for Sandbox (S4) worlds.

The second Sandbox world (S4E) is exactly the same as the standard world (S4B), but requires that a player’s account be less than 90 days old at the time of the airline’s creation, making it a good way for new players to learn the game.

Restrictions:

1.) Political: You may not operate a flight departing from or arriving in one of the below countries if the flight also departs or arrives at one of the countries listed beneath it.

Cuba:

The United States of America

Gaza Strip:

Israel
The United States of America

Indonesia:

Israel

Iran:

Israel
The United States of America

Iraq:

Israel

Israel:

Gaza Strip
Indonesia
Iran
Iraq
Malaysia
Saudi Arabia
Syria
The United Arab Emirates

Malaysia:

Israel

North Korea:

South Korea
The United States of America

Saudi Arabia:

Israel

South Korea:

North Korea

Syria:

Israel
The United States of America

The United Arab Emirates:

Israel

The United States of Anerica:

Cuba
Gaza Strip
Iran
North Korea
Syria

2.) Legislative: The following airports in the United States of America place restrictions upon departing and arriving flights:

Dallas Love Field (DAL):

All aircraft with the capacity to hold more than 56 seats are limited to serving airports located in Texas, New Mexico, Oklahoma, and Arkansas. However, aircraft with a maximum capacity of 56 seats or less have no restrictions. It is not possible to configure aircraft which could potentially hold more seats, such as the 737-800, which has a maximum of 189 seats, with 56 seats in order to avoid these restrictions.

New York LaGuardia (LGA):

Flights departing from and arriving at the airport must be less than 1500 miles in length.

Washington National (DCA):

Flights departing from and arriving at the airport must be less than 1250 miles in length.

3.) Aviation Law:

Exception 1.) European Union (Post-2000):

EU-based airlines may operate flights between countries that are part of the EU. However, you can't operate flights outside from another EU country to a non-EU country. For example, if an airline was based in the United Kingdom, they could operate flights from Paris to Oslo; however, they could not operate flights from Paris to New York. The following countries are members of the EU:

Austria
Belgium
Czech Republic
Denmark (excluding Greenland)
Estonia
Finland
France (excluding overseas departments and territories)
Germany
Greece
Hungary
Iceland
Italy
Latvia
Liechtenstein
Lithuania
Luxembourg
Malta
Netherlands
Norway
Poland
Portugal
Republic of Ireland
Slovakia
Slovenia
Spain (excluding Ceuta and Melilla)
Sweden
United Kingdom

Exception 2.) Trans-Tasman Travel Agreement (Post-1983):
Airlines based in Australia or New Zealand may treat both nations as their home country, for the purposes of domestic flights, the running hubs, and the ownership terminals. However, an airline may not operate international flights from any country except their own, though flights between Australia and New Zealand are unrestricted in origin.

By the way, the DAL restriction ends on October 13, 2014. Plus, sandbox does have political restrictions.