Arbour City Geography

Lives in: World & Lore → Core Systems (or its own Locations chapter, once that chapter has more content). This is deliberately NOT a full geography document — it's the load-bearing skeleton: orientation, hull shape, and the core/sprawl distinction that every future district, landmark, and map must be consistent with. Detailed district names, the Spine gates' Sprawl nicknames, and street-level texture are explicitly out of scope for this pass — see Open Follow-Ups.

Why This Document Exists

Arbour City Geography has been sitting on every version of the directory tree as a single intimidating "Major Undertaking" — full city shape, district layout, Spine gate positions, landmarks, all at once. That framing made it feel impossible to start. It isn't. Dozens of geographic facts are already locked across other documents (Power Grid, Transport, Water & Food, the character documents) — they've simply never been spatially reconciled into one coherent shape. This document does that reconciliation first, as a skeleton, before any district gets named or any map gets drawn.

Part One — The Hull

Confirmed Dimensions (already locked, Technical Appendices)

Length: 3,200 m
Maximum beam: 420 m
End-on cross section: ~138,544 m² — explicitly described as a circular profile, mathematically confirmed (a circle of that area has a 420 m diameter, exactly matching the stated beam).

Hull Shape

ARBOUR|05 was not a uniform tube. Consistent with real deep-ocean pressure-vessel engineering (the same logic the Committee used to justify drydock construction at 3,000+ metre depths — see The Great Stripping), the hull was tapered and segmented, not a constant-diameter cylinder end to end:

Widest point (~420 m, maximum beam): the Habitation Cylinder — the midsection, where the bulk of the colonisation population and equipment lived during the voyage. This is the section whose structural mass, per existing canon, "insulated the forward reactors" during the cascade.
Forward section (narrower): command, tapering toward the bow.
Aft section (narrower): the drive section — Kugelblitz containment, R4, and R5 — tapering toward the stern, consistent with the drive assembly being jettisoned "out the aft hatch."
Colonisation equipment — distributed, not centralised. Per existing canon, the drive section is aft and "command and colonisation sections" are forward — but the colonisation equipment itself (geothermal drilling rigs, atmospheric harvester components, the solar array material) was never one large cargo bay. It sat in smaller pockets distributed throughout the forward third, each positioned near whatever system it served, rather than centralised in a single hold. This is consistent with — and is now the mechanical explanation for — why post-crash deployment was genuinely triaged piece by piece rather than all-or-nothing: each pocket had its own access point and its own surviving engineers, and each piece of equipment's post-crash fate (geothermal taps deployed within a decade, atmospheric harvesters partially deployed, the solar arrays erected but never calibrated) was decided independently of the others.
A real downstream consequence worth flagging: once a given pocket's equipment was salvaged or deployed, the empty pocket itself became some of the oldest available interior real estate in the hull-core — a pre-existing void in the original structure, distinct from anything built later by any generation. This is a strong, ready-made hook for a specific location (an old equipment pocket repurposed as a shrine, a black-market cache, an archive wing, a Branch facility) whenever the geography pass reaches that level of detail.

This tapering and pocketing is the origin of a real, physical architectural vocabulary for Arbour's oldest buildings: pressure-rated, curved, segmented construction, with reinforced ring-frame sections at intervals along the original hull, and — in places — oddly-shaped sealed voids that don't match the logic of anything built around them — visible today as load-bearing structural bones and strange "wasted" pockets in the oldest parts of the city, regardless of whether anyone living there understands them as ocean engineering or emptied cargo space. They don't. Nobody alive has seen an ocean. These details, to a present-day Arbour resident, simply read as old, heavy, "crude," over-built construction — the same way the rest of the city treats inherited procedure: followed, normalised, never questioned for its original purpose. (Direct continuity with the "ritual engineering" framing already established in World Systems' Azure Branch material.)

Scale Check — Forward Mass vs. Aft Drive Section

A scaled side-profile pass (using the existing reactor frame-position data — R1 at Frame 12, R2 at Frame 28, R3 at Frame 67, R4 at Frame 112, R5 at Frame 134) confirms something the prose alone left ambiguous: R1 and R2 sit roughly 1,900+ metres from R4 and R5 along the hull's 3,200 m length. An early pass at this diagram connected that distance with a thin, empty service spine — which solved the distance problem but created a new one: a kilometre-plus of dead, wasted, structurally thinner space makes no engineering sense in a vessel built to survive both deep-ocean assembly pressures and relativistic flight stress, and it isn't what the existing text actually says.

The corrected version uses existing canon directly. Technical Appendices already states that "the massive liquid coolant reserves and secondary reactors (R1, R2, R3) were placed at the forward section to act as kinetic and radiation shielding" — meaning that stretch of hull was never empty. It's a full-width, mass-loaded coolant reserve and shielding section, running from the back of the Habitation Cylinder to roughly R3's position. This does three things at once: it removes the "dead space" problem, it gives a physical, geometric reason for R3's documented status ("partially functional... took the edge of the surge" — R3 sits at the edge of the shielded zone, fully protected reactors further forward, the drive section's burst reaching the rest), and it means the only genuinely narrower stretch of hull is a short service taper between the shielding mass and the aft drive bulge — not the entire forward-to-aft distance.

Worth keeping this firmly in mind for any future cross-section or map work: the forward section (command, Habitation Cylinder, colonisation equipment pockets, coolant/shielding mass) is large, dense, and functional along nearly its full length. Only the final stretch into the drive section narrows meaningfully.

Confirmed Internal Systems

Before mapping tiers onto the hull, a complete internal-systems pass confirmed the hull is not just a shape — it's already carrying the direct ancestors of two of Arbour's three transit layers, per existing canon:

The main personnel/cargo transit corridor runs the ship's full 3,200 m length — already locked in Transport Within Arbour ("the rail network began as ARBOUR|05's internal cargo and personnel transit system"). This is why the original rail lines already "cover most of Arbour's horizontal geography" from day one: they didn't need post-crash construction to achieve that reach, because the ship itself was already that long.
The maintenance crawlway layer runs separately, beneath the main corridor, also full-length — the direct ancestor of the maintenance tunnels / the warrens, per existing canon ("the original service infrastructure of ARBOUR|05... built into every section of the ship").
The Kugelblitz sits inside the aft drive section, alongside R4 and R5, consistent with being jettisoned "out the aft hatch."

This matters for the cross-section below: the original transit corridor doesn't just happen to run through the hull-core's territory — it is the hull-core's oldest infrastructure, still tracing the same path it always did, just repurposed and extended over centuries rather than newly built.

Orientation — "A Skyscraper Standing"

This corrects an earlier draft of this document, which had the ship lying flat on its side. That version doesn't hold up: the original personnel/cargo transit corridor ran the ship's full 3,200 m length, fore to aft — and a corridor like that, on a hull lying flat on its side, would stay at one constant height along the ground. It could never have organically supported a tier system that climbs from Sprawl to Luminary, because nothing about it ever climbed.

The corrected version: the ship came down steeply angled, effectively standing rather than lying flat — bow upward, stern down, closer to vertical than horizontal, though not perfectly so (a genuinely uncontrolled ballistic descent, per Kugelblitz Jettison Mathematics, would not produce a perfectly clean right angle). This means the 3,200 m long axis is the ship's height, not its footprint — and that single change resolves several things at once rather than introducing new ones:

The original transit corridor, running fore-to-aft, now runs bottom-to-top. It was always the ship's primary spine of movement; after the crash, that same infrastructure is exactly what a climbing tier system needs, with zero retrofitting required to explain why it already reaches every level.
The forward section (R1, R2, the Habitation Cylinder, the coolant/shielding mass) is now the top of the structure. This matches existing canon directly: R1 already "powers the Luminary and upper tiers almost exclusively," R2 already powers "the Meridian Districts and mid tiers" — the forward reactors were always the ones serving the upper city, and now the geometry explains why, instead of that being a coincidence sitting beside an unrelated orientation.
The aft drive section (R4, R5, the Kugelblitz) is now the bottom, at or near ground level — consistent with the drive section taking the worst of the impact, the EM cascade detonation, and the debris field forming around that lower section while the better-protected forward structure higher up stayed comparatively intact. The debris field sitting apart from the habitable hull-core, previously asserted without a clean physical reason, now has one: the bottom of the ship hit hardest and is the part most thoroughly fused with the wreckage and the widened reality tears.
R3, "partially functional... took the edge of the surge," sits geometrically between the two — consistent with a position partway up the structure, neither fully shielded like R1/R2 nor destroyed like R4/R5, and a natural fit for Meridian's in-between power profile.

The ~420 m beam — the hull's maximum width — is now read as the structure's footprint at any given height along that climb, rather than its total climbable height. This is, if anything, a more generous reading than the old one: a tier's usable floor area is bounded by a 420 m cross-section, not by a height ceiling that was never going to support multiple distinct tiers to begin with.

Of the full 3,200 m length, only the upper stretch is currently habitable — current built-up height is ~200 m from the top, with the remainder toward the base buried, structurally compromised, or sealed off, consistent with the Vault sitting "approximately 340 metres below Arbour's current surface level" (see Power Grid) — a depth that now reads naturally as further down the original ship's length, toward the stern, rather than an unrelated buried pocket.

Part One Conclusion — The Full Hull-to-City Cross-Section

With the hull's internal structure, the corrected shielding mass, the corrected orientation, and the scattered debris field all reconciled, the present-day cross-section resolves as follows:

Luminary sits at the literal top of the standing hull — the highest occupied point of the ~200 m built-up stretch, directly around the old forward Habitation Cylinder and shielding mass.
The Spine sits immediately beside it, at that same top section — a single central pentagonal complex, not distributed across the city. This is now locked (see Transport Within Arbour); previously the only genuine Tier 1 blocker remaining in the project.
Meridian Districts wrap the structure below Luminary, descending around its sides toward ground level — the mid-section of the standing hull, around R3's position.
The original transit corridor still traces through the hull-core along this same vertical run — the rail network's oldest lines climb where the ship's own fore-to-aft corridor always ran, now read top-to-bottom instead of end-to-end.
The Sprawl sits at and around the base of the standing hull, at ground level, spreading outward onto ordinary surrounding land. Whether it's symmetric in all directions around the base or concentrated toward one side remains open (see below) — but its vertical position, at the bottom rather than wrapped partway up a flank, is now settled by the orientation fix.
The scattered debris field sits beneath and around the base of the structure, where the aft drive section — R4, R5, the Kugelblitz, the worst-damaged part of the ship — came down hardest and fused with the terrain and the widened reality tears already there. This is a tighter, more physically motivated relationship than the old "off to one side" framing: the debris field isn't a separate location elsewhere on the map, it's what's directly underfoot and immediately around the base of the city people actually live in, confirmed by Power Grid to extend "beneath the Sprawl's eastern districts." The debris field itself still has no single crash site or crater (see Kugelblitz Jettison Mathematics, Part Six) — it's discontinuous wreckage fused into terrain at multiple separate points around the base, with widened reality tears threading between them, rather than one footprint or one direction from the hull-core.

A scale caveat worth carrying forward, revised: the old caveat assumed the debris field sat at some unspecified lateral distance from the hull-core. With the orientation fix, the relationship is now closer and more vertical than lateral — the debris field is substantially underneath and around the base, not off across open terrain. Some lateral spread is still expected (the impact and subsequent EM cascade scattered wreckage, it didn't all settle in one neat ring), but any future map should treat the debris field as hugging the base of the hull-core rather than as a separately located site reached by significant travel. This is a meaningful change from the prior draft and should be carried into any diagram or location work going forward.

Part Two — Two Kinds of City Fabric

This is the single most important organising decision in this document, and everything else about Arbour's geography should be checked against it:

The Core — Hull-Anchored, Old, Dense

The Luminary and the Meridian Districts are built substantially on, into, and around the standing original hull. This is the oldest part of the city, dating to the first generations post-crash, and its physical geography is directly shaped by the ship's actual structure:

Luminary sits at and near the top of the standing hull — the highest physically accessible point of the original structure, the part that emerged most intact from the crash, closest to undamaged original architecture and to R1.
Meridian Districts occupy the sides and mid-elevations of the standing hull, descending from Luminary toward ground level — consistent with R2 (which powers the Meridian Districts) and with the Upper/Lower Meridian split already established in the power allocation table.
This core is geographically compact relative to its population density, consistent with "vast and fragile" original rail infrastructure that "covers most of Arbour's horizontal geography" despite the hull itself being a fraction of the city's total footprint today — the original corridor now runs vertically through this core, with horizontal rail spurs branching outward from it at each tier level to actually reach a tier's living and working spaces.

The Sprawl — Outward Growth, Younger, Organic, and Closer to the Base Than Previously Assumed

The Sprawl is not mapped onto the upper or mid-elevations of the standing hull. It is centuries of later, more organic growth spreading outward at and around the base of the original structure, onto the surrounding land beyond the hull's footprint — consistent with:

"Sprawl" as a name (something that spreads outward at ground level, not something built partway up a structure).
The Sprawl's defining qualities already established elsewhere: widest species diversity (the demographic least represented in the ark's original passenger manifest, per World Systems, has the least claim to space inside the old hull-core and the most reason to be building new, outward), the most informal/improvised economy, dozens of distinct named sub-communities like Veilan with their own internal logic.
R5's debris field extending "beneath the Sprawl's eastern districts" (Power Grid) — this now reads as a tighter, more direct relationship than previously framed: the debris field sits beneath and around the base of the standing hull, exactly where the aft drive section came down hardest, and the Sprawl's eastern districts grew up directly on and around that same ground. The Sprawl isn't built on a separate crash-affected area reached by distance from the hull-core — it's built immediately around the base of it, on the part of the wreck that's most thoroughly fused with the debris field.

The Sprawl's "underground, hot" rail lines (Transport) run beneath this outward, ground-level growth — tunnelled beneath the later, organically-grown surface construction, running close to R5's debris field and the structural core's waste heat, which is a real, direct engineering reason for the heat (proximity to buried, still-warm wreckage and power infrastructure converging at the base of the hull) rather than depth inside the original ship.

Why This Split Matters

This gives Arbour two genuinely different kinds of architecture, not just two wealth levels wearing different paint:

Core (Luminary/Meridian): ocean-pressure-vessel bones — curved, segmented, over-built, ring-framed, occasionally producing spaces that don't make sense by ordinary architectural logic (a load-bearing wall far thicker than it needs to be for a building this size; a sealed, circular hatch-door repurposed as a vault or shrine; corridors that curve in ways nothing about the city's current function explains). Read by residents — even upper-tier residents — as simply "old" or "ancestral," never as "built for an ocean," because nobody currently living has the framework to read it that way.
Sprawl: built by hand, by need, by salvage, over generations, on ordinary land, using whatever materials and techniques each generation had — including, per Transport, entire repurposed decommissioned rail carriages (Veilan's eastern wall). No inherited pressure-vessel logic. A fundamentally different, younger architectural language.

This split also gives a future scene a genuinely strong, specific image: a Sprawl resident encountering the hull-core's "primitive," over-built, ocean-rated construction for the first time and reading it as ancestral, crude, or unsettling — without any character in the room understanding why it's actually shaped that way, since the ocean Project Arbour fled across no longer exists in anyone's living memory or oral tradition this side of the crossing.