DEVELOPMENT SNAPSHOT #67 — State Cargo Takes to the Air: Dock-to-Dock Routes and the Break-Even with Land

In a world where the sea is poisoned, the standard way to move goods over long distances is through the air. Airships fly at safe altitudes, taking off from and landing at docks. Until now, though, only military supplies could use air routes in the game; national stockpiles and raw materials for state-run factories went overland (or by sea where conditions allowed).

This round of development (stage 2a of WLD-007, six commits) opens the air to state cargo. Air routes between state-run docks are now generated automatically, and the game compares "overland" with "land, then air, then land" on both freight cost and expected losses. It also decides how long cargo waits when no flight can be booked, and how many docks and aircraft each country gets at the start of a new game.

The values in this article are current development values (calibration v2) and may change with further tuning.

Air routes connect state-run docks

Air routes are generated for every pair of operating state-run docks in the same country. Each route is the shortest path over the country's own provinces and the sea, never through another country's airspace, because there is no way to store overflight permission yet. Pairs that cannot be connected through the country's own airspace get no route, and straight-line distance is never used as a substitute.

The route list is not saved. It is derived from the map and the docks, always with the same result, and kept in memory. When borders change, a dock is damaged or a province is occupied, the change in inputs is detected and the routes are rebuilt.

Before connecting air routes to daily logistics, the reservation, arrival and cargo-handling steps of air transport stopped copying the whole map document, and reservation lookups that scanned every entry were replaced with indexes proportional to the number of entries. More air cargo should not make each day slower to compute.

Comparing "land-air-land" with overland on cost and loss

This applies to state cargo: government stockpile procurement and raw-material replenishment for state-run facilities. A route that goes overland from the sending province to the departure dock, by air between docks, and overland again from the arrival dock is compared with the existing overland route (and conditional sea routes). Private cargo still uses only land and sea.

The first key in the comparison is freight cost plus expected loss (international price times loss rate), since air cargo is far less likely than wagons to be lost to bandits on the way. Per unit of resource:

• 30 km: overland 0.06 (0.3% loss) / air 0.065 (0.06% loss)
• 100 km: overland 0.20 (1.0% loss) / air 0.17 (0.2% loss)
• 400 km: overland 0.80 (4.0% loss) / air 0.62 (0.8% loss)
• 800 km: overland 1.60 (8.0% loss) / air 1.22 (1.6% loss)

Air freight is 0.0015 per km plus cargo handling at the departure and arrival docks (0.01 each). On freight alone, air is cheaper beyond about 40 km, and counting losses it wins at even shorter distances. It is also faster: 800 km a day by air, against 100 km a day overland between regions.

With the first values, nobody chose the air

Calibration v1 set dock handling at 0.10 per dock, putting the break-even point with overland transport at about 400 km. But resource prices in the actual starting data (international prices of 0.64 to 2.79) are small compared with freight, so the difference in losses alone never made air the choice. Calibration v2 lowered dock handling to 0.01 and removed the handling loss at docks. Air loss (0.00002 per km) is now lower than overland loss (0.0001 per km) at every distance.

There was one stumble along the way. When calibration v2 was merged, the patch passed to the PC was the version from before handling was lowered, so handling stayed at 0.10. The next commit set it to the approved 0.01 and brought the documents and tests in line.

On freight alone, air is sometimes slightly more expensive. Between the Valza Empire's starting docks, air costs 0.344 over 183 km and overland 0.339 over 169 km. But the loss rates are 0.61% and 1.69%, so once expected losses are added, air is cheaper. Between the starting docks in the default data, all 26 resources choose the air.

No flight today: wait, or switch to land?

Even when air is chosen, a booking can be refused because the dock lacks handling capacity or no aircraft is free. The cargo does not switch to land that same day. It stays as an open request, and the air booking is retried every day.

It switches to land on the day the waiting time reaches "overland days minus air days" (at least one day): the point where waiting longer means the air shipment would no longer arrive before an overland one. Cargo for an island with no land connection keeps waiting for the air. Waiting records are saved only while something is waiting, so saves with no waiting cargo keep the same format.

Docks and aircraft in a new game

The default starting data had no state-run docks and no transport aircraft, so not a single air route could exist. Now, only when a new game starts, each of the four major countries gets two state-run docks (in the capital region and one other region) with one transport aircraft each, eight aircraft in total. The air distance between the two docks is about 147 km for the Windkeeper States, 271 km for the Orsea Principalities, 169 km for the Turem Federation and 183 km for the Valza Empire.

The aircraft model's mission range is 240 km, shorter than calibration v1's break-even distance of about 400 km, which would make cargo flights pointless. Cargo flights therefore use a transport operating range of 1,200 km (two days or less at 800 km a day), while mission and gunship range checks still use the model's own value. These placements happen once at the start of a new game; loading a save never adds aircraft.

Not done yet

Private cargo and privately run docks do not use air routes yet. Generated routes have no weather, route capacity or overflight rights, and they never connect to another country's docks. In the first 31 days of a default new game measured so far, no state cargo has actually been dispatched by air. When the first flights really take off is the next thing to check.

The aircraft behind air routes: Ashwind Chronicle Developer Blog #32

How transport moves the numbers: DEVELOPMENT SNAPSHOT #48

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