City Network

§ To work at peak efficiency, all of your cities should be linked together in a "trade network" (symbolized by ). This allows the cities to receive the full benefits of your civilization's resources - both domestic resources and those received through trade.
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Elements of the City Network

§ Your city network can be made up of roads and railroads, rivers, coastal squares, and ocean squares.
§ Roads and Railroads
§ Cities may be linked together by road and railroads, as long as the road/rails stay within your borders or neutral territory.
§ Rivers
§ Cities on the same river are linked together as long as the river between them stays within your borders or in neutral territory.
§ Coastal Squares
§ Cities on the coast are linked together as long as the coastline between them stays within your borders or in neutral territory and you have the Sailing technology.
§ Ocean Squares
§ Cities can always connect via ocean squares in your territory. If the ocean squares are in neutral territory, then you need the Astronomy technology in order to use them in your network.
§ Combined Networks
§ Your network may consist of a combination of the above types of links. City A may link to City B via coastal waters. Then City B links to City C via road. City C links with City D via river. And so on. In the above example, all of the cities are linked.
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Resources and the City Network

§ In order for resources to be shared by multiple cities, they must be connected by road, rail, or river to a city network - then, all cities on that network share the resource.
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Trading Resources

§ All resource trade must go through your capital city. If you wish to trade one of your resources to another civilization, then that resource must be connected to the capital city via a network link. If you receive a resource in trade from another civilization, that resource is assumed to be in your capital city. Only cities that are connected to your capital can enjoy the benefits of that resource.
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Connection to the City Network

§ Cities that are connected to the city network will have the symbol displayed next to them on the world map. If this icon does not appear next to one of your cities, it is not sharing in the benefits of the rest of your civilization!