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 — NEW, this session

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 (NEW, this session — full hull pass)

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 on Its Side"

The ship came down lying on its side — its long axis (3,200 m) running roughly horizontal across the landscape, not standing on end. Per Technical Appendices, the crash was genuinely uncontrolled (Wei dead, nobody steering), so the final resting orientation was not chosen by anyone; it is simply where 2.7 × 10⁸ kg of structural mass happened to settle. This means the ~420 m beam — the hull's maximum width — is, after the crash, effectively read as the ship's height: the tallest dimension of the wreck as it lies on the ground, rather than its length. Not all of that beam is currently habitable — current built-up height is closer to ~200 m, with the remainder buried, structurally compromised, or sealed off (consistent with the Vault sitting "approximately 340 metres below Arbour's current surface level" — see Power Grid).

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

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

Luminary sits at the literal top of the fallen hull's curve — the highest point of the ~200 m built-up arc, directly above the old Habitation Cylinder and forward shielding mass.
Meridian Districts wrap the sides of that same curve, descending toward ground level on both flanks.
The original transit corridor still traces through the hull-core along this same arc — the rail network's oldest lines run where the ship's own corridor always ran.
The Sprawl spreads outward on ordinary surrounding land, on at least the eastern side of the hull-core and very plausibly the western side as well — though only the eastern Sprawl's relationship to the debris field is explicitly locked in existing canon (see below); a western Sprawl's existence is a reasonable working assumption, not yet a confirmed fact, and should be treated as open until deliberately decided.
The scattered debris field sits separately from the hull-core entirely, off to one side, confirmed by Power Grid to extend "beneath the Sprawl's eastern districts" — meaning the debris field and the hull-core are two distinct things in two distinct places, not one footprint. The debris field itself has no single crash site or crater (see Kugelblitz Jettison Mathematics, Part Six) — it's discontinuous wreckage fused into terrain at multiple separate points, with widened reality tears threading between them.

A scale caveat worth carrying forward: any diagram compact enough to show the hull-core and the debris field together necessarily compresses the real distance between them for readability. No real-world distance between the two has been locked yet — "an unremarkable stretch of Cordis" is deliberately vague in the existing canon, and this document doesn't resolve it. Treat any future map's apparent proximity between the core and the debris field as illustrative, not a distance claim, until a dedicated geography pass sets real figures.

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 curve of the original fallen 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 fallen hull's curve — 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 hull's curve, 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 Sprawl — Outward Growth, Younger, Organic

The Sprawl is not mapped onto the lower curve of the buried hull. It is centuries of later, more organic growth spreading outward onto the surrounding land beyond the original hull's footprint entirely — consistent with:

"Sprawl" as a name (something that spreads outward, not something compressed into a buried arc).
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 is consistent with the Sprawl being built on surrounding crash-affected land, not on the hull itself, since R5's debris is part of the scattered field outside the main hull mass, not inside it.

The Sprawl's "underground, hot" rail lines (Transport) are not underground inside the old hull — they're underground in the more conventional sense of tunnelled beneath later, organically-grown surface construction, running close to R5's debris field and the structural core's waste heat, which is a separate, real engineering reason for the heat (proximity to buried, still-warm wreckage and power infrastructure) 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.

Open Follow-Ups

[ ] Exact present-day footprint and scale of the Sprawl relative to the hull-core — how far outward has three centuries of growth actually spread? Needed before any map can be drawn.
[ ] Whether the Sprawl is symmetric (both sides of the hull-core) or concentrated on one side. Only the eastern Sprawl's relationship to the debris field is explicitly locked in canon; a western Sprawl is a reasonable working assumption used in this session's diagrams, but not yet a deliberate decision. Should be resolved before any map treats it as settled.
[ ] The five Spine gates' actual geographic positions — established as "a pentagon arrangement," but not yet placed relative to the hull-core/Sprawl split established here. Worth deciding whether all five sit within the hull-core, or whether some reach out toward Sprawl territory.
[ ] Where exactly the Tabularium, the main Transit Hub, and other named locations (Mosswood's stall, Veilan) sit relative to this skeleton.
[ ] The Spine gates' Sprawl nicknames — still an existing placeholder from Transport Within Arbour, unresolved.
[ ] A specific, named visual/architectural detail or two for the hull-core's "ocean-vessel" construction — e.g., a specific sealed circular hatch, a specific over-thick wall — worth designing deliberately for at least one or two locations before this shows up in prose, so it isn't generic.
[ ] Precise vertical figures — exact metres for Luminary's elevation, Meridian's range, and how the "~200 m currently built-up of the 420 m beam" breaks down by tier, once a fuller geography pass is ready for that level of detail.
[ ] This document deliberately does NOT yet address: district names beyond Veilan and the Sprawl/Luminary/Meridian tier labels, the Badlands' relationship to the city's edge, or any map artifact. Per the original scoping conversation, those are separate, later sessions building on this skeleton.