Trade

As with exploration, espionage, terrain improvement, city founding and diplomacy, the Civilisation model for trade requires laborious pushing of units around the map. The player interventions in trade should be as follows:

• • Construction of infrastructure (roads, railways, canals, ports, marketplaces, etc) that promote trade.

  • Setting the tax rate on imports/exports per trading partner (higher tax gives more revenue but reduces volume, also diplomatic impact) (this also affects flow across the country)

  • Piracy

  • Banning imports/exports per trading partner (as a diplomatic measure) (this also prevents flow across the country)

  • War (reduces trade as a consequence)

  • Build monuments (promotes trade via prestige)

There was no trade between the Incans and the Aztecs. As such, the trade model should limit trade based upon regions that are relatively impassable. For your example, no trade routes should for over desert tiles that don't contain oases, or over tundra, or over dense rainforests.

Commodities

Can trade be modelled without modelling commodities? The disadvantage of commodities is that it can create too much of an imbalance, particularly where these are one-commodity-per-tile. A potential solution is to have multiple commodities per tile, which should reduce imbalance.

Passage

Trade that passes across the country is treated as an import and export.

Instantaneous

Assume trade is instantaneous. So the impact of actions upon trade levels are instantaneous.

The data

For each province, each turn, for each commodity:

• • value of exports to every other (known) province of the world

  • route that it takes

  • value of demand

This could be quite computationally intensive, as it would require iterative calculations such that local demand is satisfied first (or perhaps demand from rich provinces).

Can show trade on the map as a layer, with the width of the arrow showing the flow. This will highlight trade chokepoints, which are strategically important.

The value of exports to every other province in the world is related to:

• • distance (travel time)

  • populations

  • relationships

  • diplomatic status (war/peace)

  • active conflict (i.e. the presence of military units)

  • piracy

  • trade rates

  • trade bans

  • tech level

  • infrastructure (speed/latency)

  • infrastructure (capacity/bandwidth)

There is only one route used from one province to one other (this may not be the same in reverse). The route is dependent upon the variables above, with the exception of population.

Trade pact

Agreement for one Country to drop import tax to X% if the other drops import tax to Y%.

What do we want the trade model to include?

• • tax - definitely

  • diplomacy - definitely

  • currencies and exchange rates - probably not

  • balance of payments - probably not

  • impact on GDP - definitely

A highly abstracted trade model

A potential highly abstracted trade model would be to have all production of various commodities (including excess food production) automatically converted to "production units" at the market rate. That market is determined by the sum of all the trading relationships between all the players (whether trade is allowed by treaty, and whether it is possible, given blockades).

Key principles for trade

For a proper trade model, the following key principles apply:

• • location matters (location of production, location of consumption)

  • supply and demand matter

  • every commodity must have a mechanism of construction and of consumption

  • commodities matter (it is necessary for something to be in one place but not another in order for trade to happen)