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.

Who Actually Built the City — ARC's Hand in the Hull-Core

This addresses a real, worth-asking question: three centuries of deconstruction, reshaping, and floor-levelling work (see The Arbour Hull Core, "Why the Floors Are Level") is an enormous, sustained engineering effort. Who actually did it, and with what?

The answer doesn't require inventing new equipment or a new system. The colonisation equipment already established above — geothermal drilling rigs, atmospheric harvester components, the solar array deployment hardware, and by clear extension the structural cutting, shaping, and assembly systems any genuine colonisation effort would also have needed — was never meant to build a single static ship-shaped structure. It was built to deconstruct and reconfigure, to turn a vessel into the bones of a settlement. That work was never going to stop just because the colonisation plan itself was overtaken by crisis; it simply changed what it was reshaping the ship into.

And that work was never purely automated, and it didn't stay purely human either — the balance between the two shifted, generation by generation, in a direction worth being deliberate about. ARC — Arbour's ship-derived system intelligence, already established as "Autonomous Routing & Control," originally built to handle navigation and system routing aboard ARBOUR|05 — had a scope that extended naturally to directing colonisation deployment and construction logistics as well, not navigation alone. This is not a new capability invented for this document; it follows directly from what "Autonomous Routing and Control" was always going to mean for a ship explicitly built to become a colony.

Early generations leaned on ARC heavily, with surviving engineers who understood the original systems working with it directly: deploying geothermal taps, partially deploying atmospheric harvesters, erecting solar arrays, levelling the first generations of habitable deck space, directing structural cutting and reinforcement as the original hull was slowly reshaped into something people could actually live in long-term. In this period, ARC's instructions carried real, earned authority — checked, understood, and largely correct.

That balance did not hold. Per existing canon, ARC's memory core degrades non-linearly over centuries, including corruption it cannot always detect — and as that corruption deepened, and as fewer people remained alive who'd ever understood the original systems well enough to catch ARC's errors, trust in its construction-direction role eroded the same way trust in everything else inherited from the founding generation eroded: not through one dramatic failure, but through a slow accumulation of instructions that turned out to be wrong, structures that didn't make sense once finished, plans that referenced systems that no longer existed. Later generations increasingly did the work by hand, by accumulated practical knowledge, rather than by ARC's direction — the same self-taught, salvage-and-experimentation competence already established as the Sprawl's defining trait ("descendants of engineers, self-taught through salvage and experimentation... arrived at understanding from below, through necessity and curiosity, rather than from above through controlled transmission") now running in parallel inside the hull-core as well, not just in the Sprawl. By the present day, manual, hands-on, hard-won structural competence — passed person to person, the way the Sprawl already passes down which taps are stable and which sections will shed first — is the dominant mode. ARC is still occasionally consulted, still occasionally followed, but it is no longer trusted the way it once was, and the people doing the actual levelling and reshaping work today are far more likely to be relying on what they personally know about how this section of wall behaves than on anything ARC tells them.

The trouble is the same trouble ARC has everywhere else, and its damage is mostly historical now rather than ongoing. Per existing canon, ARC's memory core has degraded non-linearly over centuries, including corruption it cannot always detect — it sometimes issues instructions based on false memory, instructions that, during the era when ARC's direction still carried real authority, were followed because nobody at the time understood the system well enough to question it. That earlier trust is what left a mark: a deconstruction crew directed toward a section that didn't need it, a structural change made on a corrupted memory of what the original colonisation plan specified, a space sealed off for reasons nobody now alive can reconstruct. The people who eventually stopped trusting ARC's construction direction couldn't undo what earlier generations, trusting it, had already built. The errors are baked into the structure now, indistinguishable from deliberate human choice to anyone living today — which is precisely why the present generation relies on hands-on, hard-won knowledge of how a given section actually behaves, rather than on records of why it was built that way in the first place. Nobody currently alive can fully separate, in the hull-core's physical fabric, what reflects a real human decision from what reflects ARC's older, corrupted instructions, still standing because nobody since has had reason or resources to tear it back down and start over.

This is the same texture as everything else inherited and unexplained in the hull-core — just now extended to genuinely include the possibility that some of it was never decided by a person at all, and the further possibility that the people who eventually noticed something was wrong simply built around it, by hand, rather than ever finding out why.

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 — "The Long Incline"

This corrects an earlier draft of this document, which had the ship standing nearly vertical, like a fallen skyscraper propped upright. That version solved a real problem (a flat-lying corridor can't drive a climbing tier system) but overcorrected: it didn't actually need to be that steep, and a closer look at what "steep" means for an object 3,200 m long shows the standing-tower model was solving for the wrong constraint.

The actual constraint is simple: the original transit corridor needs enough vertical rise along its length to support a climbing tier system. It does not need to look like a standing tower to do that. At a genuinely shallow-looking lean — roughly 15-20° off horizontal, the kind of angle that would read, to the eye, as "mostly lying down, propped up at one end" rather than "standing" — the ship's full 3,200 m length still produces close to 900-1,000 m of real vertical rise. That is more than enough: the city's currently built-up, habitable stretch only needs about 200 m of that rise, a fraction of what even a shallow lean provides.

The corrected version: the ship came down at a shallow angle, roughly 15-20° from horizontal — closer to lying down than standing up, but not flat, and not symmetric end to end. Bow up, stern down, the same as before — but "up" here means propped at a shallow rise along a long incline, not a near-vertical lean. This means the 3,200 m length now spans a long incline, not a tower: roughly 3 km of horizontal run, climbing to perhaps 900-1,000 m of vertical rise at the high end. This single change resolves the same things the standing-tower model resolved, while also fixing two things the tower model strained against:

• The original transit corridor, running fore-to-aft, now climbs the incline rather than climbing a tower. It was always the ship's primary spine of movement; after the crash, that same infrastructure still does exactly the job a climbing tier system needs — it just climbs a long hill rather than a vertical shaft. 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 high end of the incline. This still matches existing canon directly: R1 powers Luminary and the upper tiers, R2 powers Meridian and the mid tiers — the forward reactors were always the ones serving the upper city, and the geometry now explains why with a more generous, more physically plausible shape than a tight vertical stack ever offered.
• The aft drive section (R4, R5, the Kugelblitz) is now the low end of the incline, at 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 end while the better-protected forward structure further up the slope stayed comparatively intact.
• R3, "partially functional... took the edge of the surge," sits geometrically between the two ends — consistent with a position partway up the incline, neither fully shielded like R1/R2 nor destroyed like R4/R5, and a natural fit for Meridian's in-between power profile.
• The Sprawl's cramped footprint problem from the standing-tower model is gone. A tower's base, even un-tapered, was always going to be a tight several-hundred-metre circle — uncomfortably small for the tier explicitly described as the most populous and most crowded. A long incline gives the Sprawl real room: it now sits along a multi-kilometre base and lower slope, not squeezed around a narrow tower's foot.
• The eastward debris-field asymmetry is now simpler to explain, not more complicated. Under the standing-tower model, "east" required reasoning through a subtle multi-axis tumble whose footprint-level effect was almost too small to matter. Under the incline model, "east" can simply be the literal downhill direction — the direction the aft section's wreckage broke away and slid or scattered toward as the ship came down. The lean itself does most of the explanatory work now, rather than needing a separate, finely-tuned tilt argument layered on top of it.

The ~420 m beam — the hull's maximum width — remains the structure's footprint at any given point along the incline, the cross-sectional width perpendicular to the slope rather than the slope's own length. A tier's usable floor area is still bounded by that 420 m cross-section; what's changed is how much of the ship's 3,200 m length that cross-section needs to travel along to gain real elevation.

A note worth flagging explicitly, since it's the kind of thing a reader will reasonably wonder: an incline this real (~17°) does not mean residents spend their lives walking on a slope. The original decks were built perpendicular to the ship's long axis and came to rest tilted at that same angle relative to true ground-level — a real, felt tilt, not a subtle one. Three centuries of inherited, unglamorous correction work (building up the downhill side, re-laying floor sections) has levelled most of the long-inhabited core; newer or less-trafficked spaces are where that work is least complete. See The Arbour Hull Core (Prose & Voice), "Why the Floors Are Level," for the full sensory and narrative treatment — this is exactly the kind of inherited-but-corrected texture that document already specialises in.

Of the full ~3,060 m horizontal run, only the upper stretch is currently habitable — corresponding to the same ~200 m of vertical rise already established, which now translates to roughly 650-700 m measured along the slope itself from the high end. The remainder of the incline, descending toward the low end, is 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 still reads naturally as further down the original ship's length, toward the stern, just now reached by descending a long slope rather than dropping straight down a shaft.

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

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

• Luminary sits at the literal high end of the incline — the highest occupied point of the ~650-700 m built-up stretch (measured along the slope), directly around the old forward Habitation Cylinder and shielding mass.
• The Spine sits immediately beside it, at that same high end — 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 occupy the middle stretch of the incline, between Luminary at the high end and the Sprawl at the low end — descending along the slope rather than wrapping around a tower's sides, around R3's position.
• The original transit corridor still traces through the hull-core along this same slope — the rail network's oldest lines climb where the ship's own fore-to-aft corridor always ran, now read as a long ascent up the incline rather than a vertical shaft.
• The Sprawl sits at and around the low end of the incline, at ground level, spreading outward onto ordinary surrounding land. The incline orientation gives the Sprawl real room to spread — a multi-kilometre base and lower slope, not a tight ring around a tower's foot. Whether it's symmetric in all directions from that low end or concentrated toward one side is addressed below — but its position at the low end, rather than wrapped partway up a tower's flank, is settled by the orientation fix.
• The scattered debris field sits at and beyond the low end of the incline, where the aft drive section — R4, R5, the Kugelblitz, the worst-damaged part of the ship — broke away and came down hardest, fusing with the terrain and the widened reality tears already there. The debris field isn't a separate location elsewhere on the map; it's what's directly underfoot and immediately around the low end 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, with widened reality tears threading between them, rather than one footprint.

Why specifically east, locked this session — now simpler under the incline model. The ship's lean wasn't a clean, single-axis tilt; a genuinely uncontrolled crash sequence tumbles on more than one axis at once, and the ship's final orientation is the resultant of however much it tipped along each. Under the incline model this is more straightforward than it was under the standing-tower model: "east" is, plainly, the downhill direction — the direction the incline descends toward, and the direction the aft drive section's wreckage broke away and scattered toward as the ship came down. The debris field's eastward position isn't a separate fact sitting beside the incline's lean; it's the same fact, read at the same scale. The ship came down leaning/sliding eastward; the aft section that broke away during that fall landed east and downhill of where the rest of the hull finally settled; the Sprawl, ten generations later, grew on exactly that ground, spreading out from the low end in the direction the incline already pointed. One cause, not two coincidentally aligned ones — and "east" was always the existing, locked fact (Power Grid: debris "beneath the Sprawl's eastern districts") that this mechanism now explains, not something invented to justify it.

Scale, now locked with real figures. Two separate events, already distinguished in Kugelblitz Jettison Mathematics, produce two separate scales:

• The impact/crash itself (kinetic energy at re-entry, ~323 kilotons equivalent per Part Five) is what actually scatters the bulk of ARBOUR|05's wreckage. Standard blast-effect scaling for an event this size suggests severe structural destruction within roughly 1.3–1.5 km of wherever the worst of the impact occurred, with debris and lighter damage plausible out to ~9 km — though a ballistic structure of this mass breaking apart on impact scatters wreckage by momentum and fragmentation more than a pure blast wave would, which is consistent with the existing "discontinuous wreckage fused into terrain at multiple separate points" framing rather than one neat radius. This is the broad debris field — several kilometres across, scattered rather than uniform, and now plausibly continuous with the downhill side of the incline itself rather than a separate zone reached by crossing open ground.
• The R4/R5 antimatter annihilation (4.3 kilotons, Part Six) is a much smaller, localised event within that broader scatter — severe blast damage within roughly 300–700 metres of wherever R4/R5 actually came to rest. This is the source of the widened reality tears and the Aetheris-intensity spike, not the whole debris field. The 340% post-crash Aetheris increase should be read as centred tightly on this smaller annihilation point, fading outward, rather than spread evenly across the entire kilometres-wide debris scatter.

The practical consequence for the hull-core's relationship to all this: with the incline orientation, the low end of the hull-core sits at or very near the edge of this broader debris scatter — close enough that the Sprawl's eastern districts genuinely do sit "beneath" or immediately adjacent to it, as already established, but the most dangerous, Aetheris-intense ground (the annihilation point itself) is a much smaller, more specific location within that wider zone — not coextensive with "the debris field" as a whole. This gives future scene-writing a useful distinction: most of the debris field is merely dangerous in an ordinary, structural-hazard sense (collapsed wreckage, contaminated ground, unstable footing); a much smaller area within it is dangerous in the Aetheris sense, and that smaller area is where the worst hot zones, the strangest geometry, and the most acute exposure risk should concentrate.

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 original hull's incline. 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 high end of the incline — 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 middle stretch of the incline, descending from Luminary toward the low end — 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 extended along the slope rather than compact around a tower's base, consistent with "vast and fragile" original rail infrastructure that "covers most of Arbour's horizontal geography" — the original corridor runs the length of the incline 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 along the slope.

The Sprawl — Outward Growth, Younger, Organic, and Spread Across the Incline's Low End

The Sprawl is not mapped onto the high or middle stretches of the incline. It is centuries of later, more organic growth spreading outward at and around the low end 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 slope).
• 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 reads as a tight, direct relationship: the debris field sits at and beyond the low end of the incline, exactly where the aft drive section broke away and came down hardest, and the Sprawl's eastern districts grew up directly on and around that same ground, spreading from the low end in the same downhill, eastward direction the wreckage itself travelled. The Sprawl isn't built on a separate crash-affected area reached by distance from the hull-core — it's built immediately around the low end 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 incline's low end) 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

• [ ] Specific examples of ARC-directed construction gone wrong — worth identifying one or two concrete instances (a specific sealed pocket, a specific structural oddity) that can be deliberately attributed to a corrupted ARC instruction, for use as a reusable scene detail, the same way the Hull-Core document's "specific, reusable details" work for sensory texture generally.

• [ ] How much oversight of ARC's construction/deployment role survives in the present day, if any — does Azure Branch still nominally direct or monitor this work, or has it become as unsupervised and unquestioned as ARC's other functions already are per existing canon?

• [ ] Whether this connects to Silas Varran's existing ARC obsession (Five Arks Thread 1) — he is already established as closest to understanding what ARC is trying to communicate; worth considering whether his investigation could plausibly touch construction/deployment logs as well as navigation data, without overloading his existing thread.

• [x] Ship orientation corrected this session, then refined to a long incline in a follow-up session. Earlier drafts had the ship lying flat on its side; that was corrected to a near-vertical standing orientation; that, in turn, has now been corrected again to a shallow-angle incline (roughly 15-20° from horizontal — closer to lying down than standing, but propped at one end, not flat). The standing-tower version solved the original rail/tier-system problem but overcorrected — a 3,200 m object only needs ~200 m of vertical rise to support the established built-up stretch, and even a shallow lean comfortably provides 900+ m of rise. The incline model keeps everything the standing model fixed (the corridor climbs, R1/R2 sit at the high end, R4/R5 at the low end) while also solving two things the standing model strained against: the Sprawl's cramped tower-base footprint, and the need for a separately-argued tilt to explain the eastward debris asymmetry. See "Orientation — The Long Incline" above for the full correction.

• [ ] How horizontal movement actually works within a tier, now that the original corridor runs the length of a long incline rather than a vertical shaft. This document's Part Two asserts horizontal rail spurs branch outward from the corridor at each tier level — a necessary piece of geography the orientation fix requires, but only asserted in passing here, not designed. Worth a dedicated pass: where do the spurs originate per tier, how do they relate to the carriage-detachment mechanic already established in Transport Within Arbour, and do they explain the "vast and fragile... covers most of Arbour's horizontal geography" framing convincingly at the district level. (Note: the incline model makes horizontal spurs somewhat more intuitive than the standing-tower model did, since "horizontal" along a long slope is a more natural direction of travel than "horizontal" branching off a vertical shaft — worth revisiting with that in mind.)

• [ ] Exact present-day footprint and scale of the Sprawl relative to the hull-core — how far outward has three centuries of growth actually spread? The incline model gives the Sprawl meaningfully more room to work with than the standing-tower model's tight base did (a multi-kilometre low end and downhill slope rather than a ~400 m-diameter foot), which should be factored into any future figure. Needed before any map can be drawn.

• [x] Whether the Sprawl is symmetric (surrounding the base on all sides) or concentrated toward one side. ✓ Resolved, new document: The Sprawl (World & Lore → Locations & Sensory Detail). Asymmetric, concentrated east — directly following the debris field's own asymmetric shape (worst where R4/R5 actually came down). Note: that document's reasoning was built around the standing-tower model's subtle multi-axis tilt; under the incline model, the same conclusion (asymmetric, concentrated east) holds and is actually easier to justify (east is simply the downhill direction), but The Sprawl document's own physical reasoning should be revisited for consistency with the incline model — flagged as a new follow-up there.

• [x] The five Spine gates' actual geographic positions — ✓ resolved. The Spine is a single central pentagonal complex — one structure, five internal shafts — sitting at the high end of the incline, immediately beside the Luminary. Not distributed toward Sprawl territory; centralisation is the entire point of how it functions as a chokepoint. See Transport Within Arbour, "The Spine — Vertical Transit," for the full revision — that document's own language should also be checked for standing-tower assumptions now that the incline model is locked.

• [ ] Where exactly the Tabularium, the main Transit Hub, and other named locations (Mosswood's stall, Veilan) sit relative to this skeleton. The Tabularium document's lower/upper-floor split should still hold under the incline model (it was never dependent on the tower's specific verticality, just on a public/restricted split low-to-high along whatever the structure's shape turns out to be) but is worth a confirmation pass.

• [ ] 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 "~650-700 m currently built-up along the incline" breaks down by tier, once a fuller geography pass is ready for that level of detail. (Figures corrected this session for the incline model — previously stated as ~200 m of straight vertical height under the standing-tower model; that ~200 m of vertical rise still holds, but now corresponds to a longer ~650-700 m stretch measured along the slope itself.)

• [ ] 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.