Proposal:Surface=laterite

surface=laterite
Proposal status:	Proposed (under way)
Proposed by:	Julcnx
Tagging:	surface=laterite Data item
Applies to:	way
Definition:	A road, track, or path surfaced with lateritic soil: a cohesive, usually red/orange, iron-oxide-rich tropical/subtropical soil that hardens when dry but rapidly becomes slippery and potentially impassable on first wetting, then deeply plastic and adhesive under sustained rain. This proposal also includes a conditional documentation update to Tag:surface=clay to distinguish laterite from clay-mineral soils.
Draft started:	2026-04-21
RFC start:	2026-05-19

Want to see the result without reading the full proposal? Jump to how the page would look like after approval.

Note for readers: this proposal addresses a surface type found almost exclusively in tropical and subtropical regions. Readers are encouraged to read the community input from mappers with direct on-the-ground experience in these areas before forming a view.

SUMMARY

• What: surface=laterite documents the red/orange tropical road soil that mappers currently fall back to surface=dirt, surface=ground, or sometimes surface=clay for lack of a dedicated value: the broader family of iron-oxide-influenced lateritic soils, covering roughly one third of continental land area across Africa, Southeast Asia, and Latin America.
• Why it matters: Laterite has two predictable seasonal states: firm and dusty when dry; slippery and potentially impassable when wet. The wet transition is two-phase: on first rain the surface becomes near-frictionless (phase 1, black-ice scenario) within minutes, then deeply plastic and adhesive under sustained rain (phase 2). Generic tags like surface=dirt do not capture this behaviour.
• Bot context: A recurrent bot moved surface=laterite to material=laterite without adding a fallback surface=* tag; an OSH history audit confirmed 711 such transitions in Cambodia and Cameroon, leaving the surface key absent on each. The bot is now stopped. This proposal reinstates and documents the signal those migrations removed.
• Laterite is not surface=clay: the distinction is behavioural, not just geographic, and holds against any clay-dominant soil. Clay-dominant soils go plastic from the surface down when wet with no firm-base phase: a mud scenario. Laterite's iron-oxide cement keeps the base rigid while only the surface becomes near-frictionless: a black-ice scenario that surface=clay cannot encode. Laterite contains a kaolinite clay mineral fraction but is not clay-mineral-dominant; iron oxides dominate, producing the intense red/orange colour. See Why not surface=clay below. After this proposal surface=clay on roads is a rare edge case; sports courts are unaffected.
• Why "laterite" not "lateritic" or "murram": OSM surface values use material nouns, not adjectives, ruling out surface=lateritic. surface=murram is accurate but East African only. "Laterite" is the most globally intelligible term across regional names (murram, terra roxa, din daeng, rahnrahn); the scope section defines exactly which soils it covers.
• Community support: 42 mappers confirmed the field description or provided relevant regional context; 2 engaged critically with geological scope and verifiability. Respondents cover Madagascar (three independent confirmations), Cameroon, Senegal, Thailand, Cambodia, Colombia, Brazil, DR Congo, Indonesia, Kenya, South Africa, Philippines, Bolivia, Argentina, India (two independent confirmations), Ghana, and West/Central Africa, including a soil engineer with direct Cameroon field experience.
• If rejected: surface=clay is already documented and will continue to absorb laterite usage. Rejection does not produce cleaner tagging; it preserves and entrenches the existing clay/laterite conflation.

Supporting pages

Detailed background is in the supporting subpages:

• Soil science, regional names, road engineering, and field identification
• Usage data, snapshot analysis, and bot migration history
• Community input and outreach responses

Problem

Laterite is a major unpaved-road material across tropical Africa, Southeast Asia, and Latin America, yet OSM has no documented surface=laterite value.

Mappers fall back to surface=dirt, surface=ground, or surface=clay, none of which capture laterite's key characteristic: it is firm and trafficable in dry season but becomes slippery and potentially impassable within minutes of first rain, then deeply plastic under sustained wet.

A recurrent bot migration converted surface=laterite to material=laterite during a rock cleanup, without adding a fallback surface=* tag. An audit confirmed 711 such transitions in Cambodia and Cameroon, leaving the surface key absent in each case. The bot applied rock-taxonomy logic to a soil value where it does not apply: laterite on a road is always naturally formed cohesive tropical soil, not a rock-derived material. The bot is now stopped; the data gap it created remains. Full data in Proposal:Surface=laterite/Data.

Proposal

Laterite road, Basankusu, DR Congo.

Add surface=laterite as a documented value for the surface=* key on highway=* ways where the surface is lateritic soil. It is not limited to graded or maintained roads.

Fallbacks: use surface=dirt when the surface is known to be a natural soil road but the material cannot be confirmed; surface=ground when the surface type is indeterminate; surface=unpaved for imagery-only mapping; surface=compacted where the surface is a visibly engineered bound aggregate mix.

Approval also triggers documentation updates to Tag:surface=clay, Tag:surface=dirt, Tag:surface=ground, and Key:surface (see Features/Pages affected below).

Scope

In scope: laterite, latosol (terra roxa, tierra colorada), nitisol where field behaviour is indistinguishable. Regional names all map to surface=laterite as the canonical value: murram, tanah merah, cabook, din daeng (Thailand), rahnrahn (Senegambia), trocha (Latin America), tany mena (Madagascar), red earth (Tamil Nadu), and equivalents. Full list with citations: Proposal:Surface=laterite/Science.

Out of scope: Vertisol and black cotton soil (tropical/subtropical; keep surface=clay); intact ferricrete or calcrete outcrop (use surface=rock); engineered bound aggregate mix (use surface=compacted); loose red sand (use surface=sand). The field test for the compacted boundary requires both conditions together: (1) imported non-laterite material is present (crushed stone, rock fragments, gravel, or non-laterite soil visibly added to the surface); and (2) the road does not turn slippery and muddy in the rainy season. Both must hold. If either condition is not met and the surface matches laterite field observation criteria, use surface=laterite. When uncertain, use surface=dirt or surface=ground.

Verifiability

No geological expertise required. Use observable signals together:

• Tropical/subtropical setting, holds its shape when dry (not loose like sand or gravel), slippery then plastic and sticky when wet, usually red/orange: use surface=laterite.
• Firmness in dry season alone is not evidence of engineering. To distinguish from surface=compacted, both must be true: visibly imported non-laterite material present (crushed stone, rock fragments, gravel, other soil) and the surface does not turn slippery and muddy when wet. If either is not met and field observation matches laterite criteria, use surface=laterite.
• Imagery-only mapping: use surface=unpaved. Material uncertain on the ground: use surface=dirt or surface=ground. Do not guess.

Rationale

Laterite is iron- and aluminium-oxide-rich tropical soil.

The red/orange colour comes from iron oxide dominance; the plastic wet behaviour comes from the kaolinite clay mineral fraction; the firm dry hardening comes from iron-oxide cementation.

The clay mineral fraction is predominantly kaolinitic, not smectitic: smectite-dominant soils (Vertisol, black cotton) swell expansively, kaolinitic soils do not, which explains the contrasting field behaviour.

The scope extends to any iron-oxide-influenced red/orange tropical soil where field behaviour matches, including latosol and nitisol families; strict separation by soil order is not field-practical.

Laterite requires mean annual temperature around 25°C, minimum rainfall around 750 mm, and a dry season of at least 5–6 months to form; it cannot exist in temperate or fully arid zones, which is why the geographic criterion in the verifiability section is a reliable first filter.

Soil science detail and full citations: Proposal:Surface=laterite/Science.

Why surface=laterite

"Laterite" and "latérite" are the standard terms in English and French documentation across sub-Saharan Africa, Francophone West and Central Africa, and the broader tropical literature. This makes it the most globally intelligible canonical value, accommodating regional vocabulary while keeping data internationally consistent. surface=murram is accurate but East African only; OSM surface values use material nouns, not adjectives, ruling out surface=lateritic.

As a road surface, laterite takes only one form: naturally formed cohesive tropical soil. It is unambiguous in a way that rock-material terms like "granite" are not, since granite on a road could mean paving stones, sett, cobblestone, or raw rock surface.

The arguments against the main tagging alternatives are in the dedicated sections: Why not surface=dirt, Why not surface=clay, Why not material=laterite, and Why not dirt=laterite.

Likely objections and responses

• "This is just dirt": surface=dirt is a valid fallback when the surface material is uncertain. See Why not surface=dirt for why it is not the right tag when laterite is known.
• "Why this soil only": This is not a full soil taxonomy proposal; it targets one high-impact, field-recognisable case. A dedicated value for one major well-documented soil type is straightforward precedent in OSM.
• "Term is scientifically contested": The term is well-established in road engineering: a systematic literature survey on laterite road construction compiled over 1,200 references. The academic debate concerns the strict pedological definition of the hardened crust; road engineering and this proposal use "laterite" in the broader sense of the iron-oxide-rich residual soil family, which is consistent and well-documented. OSM needs reproducible field criteria, not laboratory certainty. The observable indicators (tropical setting, red/orange colour, wet-season plasticity, bonded profile) provide a usable proxy even where the pedological boundary is fuzzy.
• "Cannot verify without visiting in every season": No OSM surface tag requires year-round presence; surface=dirt and surface=mud face the same seasonal uncertainty. Verification uses observable field signals at survey time.
• "This adds complexity for routers": Routers already handle a wide range of unpaved surface values; this slots in at the same level as surface=dirt. As a distinct documented value, it gives router developers a stable handle to attach explicit wet-season penalties or advisories. surface=dirt provides no such hook; surface=laterite does.
• "Why not use surface=clay as a catch-all for any soil that turns slippery when wet": See Why not surface=clay below for the full argument, including loess and chernozem.
• "Just use surface=dirt + smoothness:conditional": Material and condition are different things: surface=laterite lets software infer seasonal risk from the material alone, without requiring wet-season observation. It also does not address the clay conflation problem, and smoothness:conditional is not yet documented practice.

Why not surface=clay

Laterite contains a clay mineral fraction (predominantly kaolinite) but is not clay-mineral-dominant. The core reason laterite cannot use surface=clay is behavioural, not geographic, and holds against any clay-dominant soil:

• Wet behaviour, phase 1 (primary distinction): All clay-dominant soils, whether smectite-dominant Vertisol in the tropics or kaolinitic or marine clay in temperate regions, go plastic from the surface down when wet: a mud scenario. Smectite swells rapidly on first contact; kaolinitic clays more gradually, but neither produces a firm-base phase. Laterite's iron-oxide cement forms by dehydration of sesquioxides during the dry season (oxidizing conditions) and releases on re-wetting, keeping the base rigid while only the surface film fails and becomes near-frictionless: a black-ice scenario. Clay-dominant soils have no sesquioxide dehydration cycle; they absorb water at the clay-mineral lattice level and deform progressively from the surface down, with no firm-base phase. Tagging laterite as surface=clay buries phase 1 permanently and produces wrong routing logic regardless of which clay soil is used as the fallback.
• Material: laterite is iron-oxide dominant; clay-dominant soils are clay-mineral dominant. These are different compositions with different physical mechanisms.
• Colour: clay minerals are naturally white to light-grey; the intense red/orange of laterite comes from iron-oxide dominance, not clay impurities. Clay-dominant road soils (Vertisol, black cotton) stay dark grey to black: that colour comes from humus bound tightly to smectite clay minerals.
• Dry behaviour: laterite hardens and holds its shape when dry due to iron-oxide cementation. Clay-dominant soils crack and crumble when dry but do not harden to the same rigidity.
• Field plasticity: clay-dominant soils, especially smectite-rich ones, make a smooth cohesive thread when rolled wet. Laterite is grittier: the iron-oxide particles and lower-plasticity kaolinite resist forming a clean thread.
• Geography (field shortcut, not the justification): lateritic soils form only in tropical and subtropical regions. Outside that range laterite is off the table, but within the tropics the behavioural distinction above is what separates it from surface=clay.
• Why not use surface=clay as a catch-all for all slippery soils (loess, chernozem): Wet behaviour alone is not a sufficient basis for a surface tag; the physical mechanism determines the routing implication. Loess is silt-dominant (typically 50–70% silt, ≤20% clay): it contains a clay fraction but its wet failure mode is collapse, not plastic deformation; the porous vertical structure loses cohesion when saturated and the surface gives way rather than deforming. Loess on roads would map to surface=dirt or surface=ground, not surface=clay. Chernozem is humus-dominant: its dark colour and field behaviour are driven by organic matter content, not clay minerals; when drier it is quite distinct from clay. Neither shares laterite's iron-oxide cementation or phase 1 behaviour. Collapsing everything slippery into surface=clay would erase those distinctions and produce a tag too broad to give routers actionable signal.

Why not surface=dirt

surface=dirt is the natural fallback, but it loses the seasonal-behaviour signal when laterite is known:

• Using surface=dirt when the mapper knows the surface is laterite discards actionable routing information. surface=dirt gives no hook for wet-season penalties; surface=laterite does.
• Wikipedia confirms laterite is not a dirt subcategory: the dirt road article places laterite roads in a category that "may be dirt roads or improved roads", explicitly not a dirt subtype; the gravel road article gives laterite and murram their own named subsection, distinct from both dirt and gravel.
• When laterite is tagged as surface=dirt, the clay/laterite conflation is not resolved: routers and renderers have no way to distinguish the two, and surface=clay continues to absorb laterite usage as an alternative fallback.

surface=dirt remains the correct tag when the surface material is genuinely uncertain on the ground.

Why not dirt=laterite

Laterite is not a subtype of dirt:

• Dirt implies an unspecified loose or bare soil surface. Laterite has a distinct composition (iron-oxide dominant), a distinct dry state (hardens and holds shape due to iron-oxide cementation), and a distinct wet state (phase 1 near-frictionless slip before deep plasticity). Encoding it as a dirt subtype misrepresents the parent category and buries the routing signal.
• Laterite roads span both natural unimproved surfaces and improved surfaces where crushed laterite is used as a road aggregate. A natural unimproved laterite track and a graded laterite road both use surface=laterite; neither is exclusively a dirt surface. surface=dirt cannot serve as the parent for both.
• Wikipedia confirms laterite is not a dirt subcategory: the dirt road article places laterite roads in a category that "may be dirt roads or improved roads", explicitly not a dirt subtype; the gravel road article gives laterite and murram their own named subsection, distinct from both dirt and gravel.
• dirt=* has no established values in OSM: it is a novel key with no consumer support, imposing higher adoption cost than adding a value to an existing documented key.
• The consumer fallback would remain surface=dirt, losing the laterite signal entirely.

Why not material=laterite

material=laterite added to surface=dirt or surface=compacted does not solve the problem:

• material=* is poorly defined for surface use: no community consensus on whether it covers geological/formation categories or construction materials. Laterite is a weathering residual with variable composition (clay minerals, iron oxides, aluminium hydroxides, rock fragments), not a discrete geological or construction material.
• The compound form does not propagate in practice: the bot migration produced 711 material=laterite transitions with zero fallback surface=* tags added, and the data gap was not repaired.
• Routers query surface=* for routing penalties and do not parse material=*: whatever base value is chosen (surface=dirt, surface=compacted) that is the signal consumers act on, not the subtag.
• surface=compacted is by definition an engineered aggregate mix. A fully accurate material=* for such a road would need to list all components (e.g. material=laterite;crushed_stone;sand), confirming that surface behaviour is the more practical mapping unit than material composition.
• surface:material=* is a lower-use alternative form with the same problems: no router or renderer parses it for routing penalties, and the consumer fallback remains the base surface=* value.
• Without surface=laterite, usage falls back to surface=dirt (routing signal lost) or surface=clay (conflation with clay-mineral soils continues). The compound tag does not produce a cleaner outcome; it just shifts where the signal is lost.

Router support

OSM tags do not require prior consumer implementation. Every documented surface=* value was unknown to routers before it was proposed; the proposal process exists to create the standard that consumers implement.

Routers handle unknown surface=* values with conservative fallbacks. GraphHopper assigns all unrecognised surface values to OTHER, its worst surface category, more penalised than surface=dirt, not ignored. Valhalla maps unknown surface inputs to kDirt internally. Neither router silently drops an unknown value; both default to maximum caution, which is appropriate for an unfamiliar surface.

A dedicated documented value gives router maintainers a stable handle to implement explicit wet-season penalties. surface=dirt provides no such hook. Without surface=laterite, these roads receive a generic dirt signal at best, or no surface signal at all where the bot migration left the surface key absent.

Post-approval outreach is planned to JOSM, iD, Vespucci, Valhalla, OsmAnd, Guru Maps and others (see Post-approval consumer outreach). Recommended implementation penalties are in the Router guidance section of the tag page preview below.

Features/Pages affected

Approval of this proposal triggers the following documentation edits. These changes are conditional on this proposal passing.

• Tag:surface=clay: replace the Roads and paths section to state that clay on roads is a rare edge case (iron-oxide-dominant soils belong to surface=laterite); add surface=laterite to See also.
• Tag:surface=dirt: add surface=laterite as a more precise alternative for identifiable tropical cohesive soil roads.
• Tag:surface=ground: add surface=laterite to the list of more precise alternatives.
• Key:surface: add surface=laterite to the examples of specific unpaved surface values.

Migration: revert bot-converted material=laterite highway ways (priority); retag surface=murram uses after local verification; retag laterite roads tagged surface=clay on highway features where confirmed. No mass-automated migration; local confirmation required. Details in Proposal:Surface=laterite/Data.

Post-approval consumer outreach

After approval, tickets will be opened at the following projects to request support for surface=laterite. This list is not exhaustive; further projects may be added as the tag gains adoption.

• Editors/presets: JOSM preset, iD (add surface=laterite as a selectable preset with label "Laterite"), Vespucci, MapComplete, StreetComplete
• Routers: Valhalla
• Renderers/tiles: OpenStreetMap Carto, Shortbread tiles, OpenStreetMap Americana
• Mobile apps: OsmAnd, Guru Maps

How the wiki would look if passed

The block below is the intended post-approval content of Tag:surface=laterite, formatted as the tag page would appear. Heading levels are shifted one level deeper than on the live page.

Tag:surface=laterite

surface = laterite
Description
Unpaved road or track surfaced with lateritic soil: red-orange tropical soil, firm and dusty when dry, slippery then potentially impassable when wet.
Group: properties
Used on these elements
Useful combination
highway=track highway=unclassified highway=path smoothness=* tracktype=*
See also
surface=dirt surface=ground surface=compacted Key:surface
Status: approved
surface=laterite $1% $1% $1% $1% More details at taginfo
Tools for this tag
taginfo · AD · AT · BE · BR · BY · CH · CH² · CN · CZ · DE · DK · FI · FR · GB · GR · HU · IE (N+S) · IN · IR · IT · LI · LU · JP · KP · KR · NL · NO · PL · PT · RU · ES · AR · MX · CO · BO · CL · EC · PY · PE · UY · VE · TW · UA · US · VN overpass-turbo QLever Sophox Postpass via overpass-turbo OSM Tag History StyleInfo

Surface tag for roads, tracks, paths, and footways surfaced with lateritic soil: a cohesive, usually red or orange-red, iron- and aluminium-oxide-rich tropical or subtropical soil. Becomes slippery on first wetting, then plastic and sticky under sustained rain, making it potentially impassable; hardens to firm and dusty in dry conditions.

Field identification

No geological expertise is required. Use multiple observable signals together:

• Geography: mostly tropical/subtropical; uncommon outside these zones.
• Colour: usually red to orange-brown; the range spans yellow-orange to deep reddish-brown. Can lighten to orange-beige when dry, darken toward brown when wet. Clay minerals are naturally white to light-coloured; intense red/orange indicates iron-oxide influence, consistent with laterite. Wet-state colour alone is non-diagnostic.
• Wet behaviour, phase 1 (first wetting): The iron-oxide cement releases on first rain, producing a near-frictionless slip layer over a still-firm base: sudden, severe traction loss before the road has visibly changed. Can develop within minutes. Affects pedestrians too: barefoot walking becomes impossible before the road visibly softens.
• Wet behaviour, phase 2 (sustained wet): Plasticity penetrates throughout: deeply sticky, adhesive to vehicles and footwear, and potentially impassable.
• Drying pattern: polygonal cracking after wet periods.
• Drainage: puddles persist longer than on sand or gravel.
• Structure: cohesive cut banks, not loose or crumbling. Deterioration takes the form of potholes in flatter or lower-traffic contexts and deep ruts in heavily trafficked zones; cohesion is retained in intact sections in both cases.

Practical rule: tropical setting + cohesion + wet-season plasticity (+ usually red/orange) supports surface=laterite. If uncertain on the ground, use surface=dirt or surface=ground; if mapping from imagery alone, use surface=unpaved.

• 
  Global extent of lateritic soils.
• 
  Wet phase 1: truck slipped on first wetting.
• 
  Wet phase 2: sticky and plastic.
• 
  Adhesion to vehicles and footwear.
• 
  Desiccation cracking after wet-dry cycle.
• 
  Cohesive cut banks with red-orange iron staining.
• 
  Firm surface, dry season.

Tagging

Recommended combinations

surface=laterite describes material identity. Add condition tags separately:

• smoothness=*: use the most common or typical conditions as the base value, not the dry-season state alone.
• tracktype=grade3 is the appropriate default for natural laterite. Use grade2 only for roads demonstrably firm year-round (approaching surface=compacted behaviour); dry-season firmness alone does not justify grade2. Note: no standard OSM tag yet exists for weather-dependent passability.

Relations to other tags

• surface=mud: for places that are wet nearly all year and never or rarely dry. Laterite alternates between firm and plastic seasonally; use surface=laterite regardless of current conditions. surface=mud applies only in the rare case where a laterite surface stays muddy year-round and never dries.
• surface=dirt / surface=ground: fallbacks when the material cannot be confirmed on the ground. surface=dirt when it is clearly a natural soil road; surface=ground when the surface type is indeterminate.
• surface=unpaved: the correct fallback for imagery-only mapping, where only the absence of paving can be confirmed.

Full tagging decision table (boundary cases, din lukrang, murram, compacted vs laterite) is in Proposal:Surface=laterite/Science.

Possible tagging mistakes

• Do not use material=laterite alone on highway=* ways where surface=laterite is known.
• Do not infer laterite from colour alone: even in tropical areas, ground-level photography or confirmed local knowledge is required to confirm the material.
• Do not use surface=laterite for loose red sand; use surface=sand.

Router guidance

surface=laterite warrants a significantly higher penalty than surface=dirt or surface=clay. In tropical regions, laterite roads are in a wet or transitional state for more than half the year: the risk window extends several weeks before and after the official rainy season, as off-season rain is sufficient to trigger phase 1. In northern Thailand, for example, trails can be slippery from April through early December, roughly eight months. The wet state has two distinct phases:

• Phase 1 (first wetting): the iron-oxide surface cement releases within minutes of rain, producing near-frictionless slip over a still-firm base. The road looks dry and hard but provides almost no traction: a black-ice scenario, not a mud advisory.
• Phase 2 (sustained wet): the surface becomes deeply plastic and adhesive, potentially impassable to all but the heaviest four-wheel-drive vehicles.

Both phases occur on roads that look passable until the moment they are not. A generic dirt or clay penalty does not capture this risk.

Examples

• 
  Thailand. Dry-season laterite track, Thung Salang Luang National Park.
• 
  Ethiopia. Red-orange laterite, dry season.
• 
  Uganda. Firm red laterite road, dry season.
• 
  Laos. Deep red-orange laterite road.
• 
  Argentina. Basalt-derived latosol (tierra colorada).
• 
  India (Kerala). Wet-season laterite track.

Counter-examples

Colour alone is not enough. Iron-stained rock, volcanic soils, and red sandstone gravel can look similar but are not cohesive or plastic like laterite. Outside tropical/subtropical settings, laterite is unlikely.

• 
  Kyrgyzstan: iron-stained crushed rock, not laterite.
• 
  Utah (BLM): deep loose sand, not laterite.

See also

• Key:surface
• Wikipedia: Laterite

---

External discussions

• OSM Community: RfC — Feature Proposal: surface=laterite
• OSM Community: Improving the wiki definition of surface=clay
• OSM Community: surface=compacted poll thread
• OSM Community: migrate rock-related surface tags to material
• OSM Community Africa: Draft proposal surface=laterite, seeking feedback from field mappers in Africa
• OSM Community LatAm: Borrador de propuesta surface=laterite, comentarios de mapeadores de campo en LatAm

Community input

Of 100 mappers contacted, 44 responded; of those, 42 confirmed the field description or provided regional context, and 2 engaged critically (raising concerns about geological scope and verifiability). Three independent respondents from Madagascar confirmed the same description; further positive confirmations came from Thailand, Cambodia, Colombia, French Guiana, Kenya, South Africa, Ghana, India, Philippines, and West/Central Africa, including a soil engineer with Cameroon field experience. Full outreach methodology and individual responses: Proposal:Surface=laterite/Community.

Comments

Please comment on the discussion page.

Changes during RfC

2026-05-25

• Summary: "Why it matters" wet transition described as two-phase: phase 1 (near-frictionless, black-ice scenario) on first rain, phase 2 (deeply plastic, adhesive) under sustained rain.
• Community input summary: French Guiana added to the region list following the talk-page confirmation received 2026-05-24.
• Preview section: fixed malformed HTML anchor (missing closing quote on id="preview") that was breaking the jump link at the top of the page.

2026-05-24

• Talk page: French Guiana field confirmation received; laterite very common on minor roads and paths; tag considered more precise than surface=ground or surface=dirt. Community annex updated.
• Talk page: StreetComplete geographic scoping raised; noted that SC quest filtering is SC's own implementation concern; post-approval SC outreach will include a suggestion to surface local names per country (murram, din daeng, rahnrahn, tany mena, etc.) drawn from the Science subpage regional vocabulary.

2026-05-23

• Respondent counts updated: 44 responded, 42 confirmed. India: second confirmation added (Auroville, Tamil Nadu); local name "Red Earth" directly corroborates the scope section entry for Tamil Nadu.
• Preview page: added "Router guidance" subsection recommending a significantly higher penalty than dirt/clay, with descriptions of phase 1 (black-ice, near-frictionless on still-firm base) and phase 2 (deeply plastic, potentially impassable). Risk window noted as more than half the year, extending several weeks before and after the official rainy season; northern Thailand example (April–early December, ~8 months) added.
• Router support section: added cross-reference to the Router guidance section of the preview.
• Rationale: added one-sentence quantification of formation conditions (mean annual temperature ~25°C, minimum rainfall ~750 mm, dry season ≥ 5–6 months) explaining why the geographic criterion in the verifiability section is a reliable first filter. Source: Charman (1988).
• "Why not surface=clay", phase 1 bullet: added sesquioxide dehydration mechanism explaining why laterite has a firm-base phase that clay-dominant soils cannot replicate (cementation forms by dehydration in dry season, releases on re-wetting; clay-mineral soils have no equivalent cycle). Source: Charman (1988).
• "Term is scientifically contested" objection: added counter noting that road engineering literature on laterite comprises over 1,200 references and the term is not contested in the engineering sense relevant to this proposal. Source: Netterberg et al. (2014).
• References: added Charman (1988), Grace (1991), and Zame et al. (2017) as direct references. Zame (2017) cited in Problem opening to anchor the Africa engineering data alongside the community outreach.

2026-05-22

• Summary: "Laterite is not clay" bullet rewritten as "Laterite is not surface=clay"; distinction now leads with the behavioural argument (phase 1 black-ice scenario vs. mud scenario), acknowledges kaolinite clay mineral fraction, links to new dedicated subsection.
• Rationale: "What laterite is" subheader removed; content flows directly into Rationale. "Why surface=laterite" bot paragraph moved to Problem section where it belongs; links to all four "Why not" subsections added.
• Likely objections restructured: "Just use surface=dirt + material=laterite" expanded into three dedicated subsections: "Why not surface=clay", "Why not surface=dirt", "Why not dirt=laterite", "Why not material=laterite". Each subsection gives full arguments including Wikipedia references, propagation failure data, and conflation-as-fallback point.
• "Why not surface=clay" subsection: phase 1 as primary distinction against any clay-dominant soil (not just Vertisol); explicitly addresses loess (silt-dominant, collapse failure mode) and chernozem (humus-dominant) as non-clay-dominant soils that also cannot use surface=clay.
• "Why not dirt=laterite" subsection: laterite spans both natural and improved road surfaces, making dirt an invalid parent category; Wikipedia references added.
• "Why not material=laterite" subsection: surface:material=* alternative form addressed; conflation-as-fallback argument added (without surface=laterite, usage falls back to surface=dirt or surface=clay).
• Problem section: bot paragraph extended to note the bot applied rock-taxonomy logic to a soil value where it does not apply.
• "Router support" subsection added: explains that OSM tags do not require prior consumer implementation; documents conservative fallback behaviour in GraphHopper (OTHER) and Valhalla (kDirt); argues that a dedicated documented value gives router maintainers a stable handle for wet-season penalties that surface=dirt does not provide.

2026-05-21

• Respondent counts updated: 43 responded, 41 confirmed (Philippines field confirmation received during RfC).
• Community annex: Philippines added to confirmed field descriptions; field description confirmed (sticky, almost impassable when wet, slow draining, mountainous/rugged terrain); local term "mud/clay" regardless of colour; respondent distinguishes this material from farm and rice-field clay.
• Compacted boundary field test hardened: wet-season behaviour (slippery/muddy = laterite, grip maintained = compacted) promoted as primary test; imported non-laterite material added as a sufficient indicator; visual pisolith check demoted to secondary.
• "Just use surface=dirt + material=laterite" objection: expanded with two additional points: (1) laterite is a weathering residual defined by formation process, not a fixed-composition material, and there is no settled consensus on whether material= covers geological categories or construction materials only; (2) the compound form does not propagate in practice (711 bot transitions, zero fallback surface tags added).
• Black cotton / Vertisol references: added "(tropical/subtropical)" qualifier in summary and scope to distinguish from chernozem, which is also dark-coloured but temperate.

2026-05-20

• "This is just dirt" objection: replaced imprecise Wikipedia paraphrase with accurate quotes: dirt-road article places laterite in a category that "may be dirt roads or improved roads"; gravel-road article gives laterite/murram their own named subsection distinct from both dirt and gravel.
• surface=mud comparison: reworded to lead with permanence ("wet nearly all year, never or rarely dry") rather than seasonality; added that surface=mud applies only where laterite stays muddy year-round and never dries.
• Aerial identification caveat: strengthened — colour alone is insufficient even in tropical areas; ground-level photography or confirmed local knowledge required.
• Respondent counts updated: 42 responded, 40 confirmed (one Colombia and one Indonesia confirmation received during RfC).
• Talk page: Indonesia field confirmation received (Rtnf); tanah merah confirmed as local name (already in scope); "bélok" noted as local term for wet-phase adhesion to footwear and vehicles; surface=dirt wiki photo confirmed as not representative of tanah merah.

2026-05-19

• Bot context: clarified the bot moved surface=laterite to material=laterite with no fallback surface=* tag added, and is now stopped.
• "Just use dirt + material=laterite" objection: expanded to explain that consumers use surface=* for routing, not material=*, that the compound tag has not propagated in practice, and that surface=asphalt over surface=paved + material=asphalt is the established precedent.
• "Adds complexity for routers" objection: clarified that a distinct documented value gives router developers an explicit handle for wet-season penalties.
• Post-approval consumer outreach plan added listing editors, routers, renderers, and mobile apps to be notified after approval.