航线代表着港口到港口的连接。
建立航道
Shipping Lanes are established for three different reasons:
- Trade Routes to an overseas market (or a market, where the land trade limit is not enough to service the trade route).
- Supply Routes for an overseas General
- Port Connections to link states (including colonies) not connected by land in a market
Each shipping lane must have its own origin and destination port. Once established it will span across a number of sea nodes and have its own individual cost in 
convoys which adds up to the country’s total convoy requirement.
It also tracks its own Effectiveness score which is based on the overall Supply Network strength and may be reduced by any local convoy damage by enemies raiding convoys done along the route.
船队
Convoys are an essential part in maintaining shipping lanes. They are produced from Ports, a government building which requires 
Clippers or 
steamers and possibly other goods such as 
Coal. Additionally puppets will provide 50% of their convoys to their overlord.
Each country has a set number of required convoys and not having enough will incur penalties on all shipping lanes. This may for example occur due to an overstretched colonial empire or hostile convoy raiders.
港口连接
In order for a state to access the goods within the market it needs to be able to trace a path back to the market capital. If this path requires it to go via the sea a shipping lane must be established to the market capital.
This must be done for every state within the market including foreign ones. Rather than a single state having its own shipping lane a group of adjacent overseas states can form a cluster with a single exit port to the market capital.
This assumes such a port exists however. If the connection is severed from either end then the overseas states cannot access the market and thus forms its own isolated enclave. Likewise if the shipping lane effectiveness is strained it will lower the accessibility of goods to and from the overseas states.
It is the market owner which must establish and pay for the port connections to all overseas market states. To somewhat compensate for this its subjects must share a portion of their convoys with their overlord. Subjects are still required to pay for their own trade and supply routes however.
The convoy cost of a port connection is influenced by the number of sea nodes and the overseas infrastructure usage. By extracting your raw materials from overseas colonial plantations and mines, while the high-Infrastructure manufacturing industries producing finished goods are located near the market capital, you can keep your Port Connection cost down - though at the expense of the development and wealth of your colonies.
供应网
And lastly when combining all the shipping lanes of a country we get its overall Supply Network. As outlined early on we derive its Strength score from the costs of all individual shipping lanes compared to the country's total supply.
If a supply network is insufficient, it will result in overseas states being partly or completely isolated from the market and it will prevent trade routes from growing further, even though they have to potential to do so. If a country has a surplus of convoys, it will increase their trade route competitiveness in proportion to the surplus.