This article is considered accurate for the current version of the game.
The supply chain in Cities:Skylines involves the production, processing and selling of various forms of "stuff" and the necessary transportation to allow this to occur. The flow of cargo through a city is as important as the flow of people.
In theory a city's supply chain can exist in complete isolation from the outside world, but in practice it is necessary to allow for exports and imports to deal with excesses and shortfalls of supply. There are various different types of cargo and cities very commonly have large volumes of imports and exports simultaneously.
From production to sales
Assuming no import or export, a unit of cargo will pass through four different buildings in its "lifetime"; a primary producer, a secondary processor, a (tertiary) generic processor, and a shop. This complete supply chain requires specialized industry for the first two steps, generic industry for the third, and commercial zoning for the last.
There are four types of raw materials: agricultural materials, forestry materials, ore, and oil. Raw materials are produced by the appropriate regions of specialized industry, when it is zoned in areas with the appropriate natural resource. Buildings which produce raw materials are easy to identify visually.
Raw materials cannot be used directly by goods-producing industries. Instead these raw materials need first to be processed. There are different processing buildings for the different types of raw material and these will only occur in zones of the relevant specialized industry. A few secondary processing buildings will emerge in areas where primary production occurs, and if specialized industry is zoned in areas without the appropriate natural resource it will consist entirely of these buildings.
If the scattered secondary processing buildings in areas of production are insufficient to process the produced material, you may wish to deliberately zone specialized industry in resource-free areas to develop more secondary processing capacity.
Generic industrial buildings require occasional deliveries of the different types of processed resource. It appears that a generic industrial building will occasionally demand a delivery of a random resource. In aggregate, a large zone of generic industry will require an approximately steady supply of all four types of processed resource.
All generic industry produces appropriately generic units of "goods".
Buildings in commercial zones receive "goods", which allows them to operate and service customers.
An exception to this supply chain are the coal and oil power plants, which consume, respectively, unprocessed ore and oil.
The most basic form of transportation of cargo is via roads. There are a variety of different cargo-transporting vehicles in the game, and there a specific vehicles for each kind of specialized industry. A vehicle which transports cargo is always owned by the delivering building; these vehicles will return to their facility once they have completed deliveries. Vehicles will only supply cargo from one building, but may deliver cargo to several customers in one round of deliveries. When viewing a delivery vehicle's info window you can see its % load, and what proportion of its load it drops off at each building.
Because the routes of cargo and people are different, a well-designed city will be able to separate the traffic of both, reducing the likelihood of congestion and intolerable noise pollution. Applying the heavy traffic ban policy to districts is one way of controlling the routes of industrial traffic. Another, is to zone commercial areas in the middle of the map, residential and industrial areas on either side of the commercial area, separating commuters and goods.
Cargo terminals are effectively public transportation for cargo, providing fast high-capacity transport options for cargo that reduces the burden on the roads. Cargo harbors, although primarily ports for imports and exports, can also be used by cargo for intra-city transportation. Road transport is required to transport cargo to and from these buildings - with the notable exception of the Cargo hub added in the After Dark Expeansion. Vehicles sent from a terminal or harbor will be owned by that building and will need to return to the facility once deliveries have been completed.
If transport problems result in cargo being unable to reach their destinations industry and commerce will not be able to function and will become abandoned.
Imports and exports
If there is an excess or shortfall at any point in a city's supply chain, for any sort of product or good, the supply chain can be supplemented with imports and exports from outside the city. These can be done via three ways:
- By road - vehicles will use the outside highway connection. Note that both importing and exporting vehicles will need to go back to where they came from after completing their delivery.
- By rail - cargo will be loaded to/unloaded from trains at cargo terminals. Trains that come into the city to import cargo can be loaded with export cargo for the return journey.
- By ship - cargo will be loaded to/unloaded from ships at cargo harbors. Like trains, a cargo ship can do both imports and exports.
There is no revenue directly accrued to the city budget from exports, nor is there a cost to the city treasury for industry/commerce importing cargo (other than the maintenance cost of cargo transport facilities). However importing or exporting goods is effectively missing out on tax revenue of the city that could have been earned had these goods been produced/processed/sold within itself.
The imports and exports of individual buildings, color-coded by type of product, can be viewed in the 'Outside connections' info view. This info view also brings up import/export statistics for the city as a whole.
At a per-building cost to the city treasury, the "Industrial Space Planning" policy doubles the goods production of industrial buildings, doubling the effectiveness of the affected buildings and their employees in contributing to the supply chain (this can also be considered as halving the number of buildings and jobs required to fulfil the same supply function). "Big Business Benefactor" and "Small Business Enthusiast" do the same for sales in high- and low-density commercial buildings respectively. When considering whether to enact these policies, mayors should also consider that these will double the per-building freight burden on the transport system.