diff --git a/docs/DOMAIN-INSTANCES.md b/docs/DOMAIN-INSTANCES.md
index 3434426..639fee7 100644
--- a/docs/DOMAIN-INSTANCES.md
+++ b/docs/DOMAIN-INSTANCES.md
@@ -125,12 +125,35 @@ inner auth AND durable outer audit, and ships exactly that separation.
 
 ### 2.6 Geospatial / OSM — geographic calibration
 
-**What OSM proves: geography doesn't break the IR.** OSM IDs are
-*already* prefix-structured (`country/region/city/street/house`), so
-the adapter is doing identity-*extraction*, not identity-construction
-— a much smaller surface than typical. Three OSM Classes (`Node`,
-`Way`, `Relation`) lift via the queued `ogar-from-osm-pbf` adapter
-(`docs/RDF-OWL-ALIGNMENT.md §10` Phase 2c). Exercises:
+**What OSM proves: geography doesn't break the IR.** OSM elements use
+**per-element-type flat numeric ID spaces** ([OSM data model][osm-dm]
+— `Node 100`, `Way 100`, and `Relation 100` are unrelated; IDs are
+not hierarchical and carry no spatial information on their own). The
+adapter therefore does identity *construction*, not extraction: it
+computes the Cesium TMS quadkey from the element's **resolved**
+geometry — only `Node`s carry coordinates directly; `Way`s and
+`Relation`s reference other elements and must be resolved through
+their members first:
+
+- **`Node`** — quadkey from its own `lat`/`lon` (the only element
+  type that carries coordinates).
+- **`Way`** — resolve the ordered `Node`-references first to get the
+  underlying lat/lon list, then take the centroid (or the smallest
+  covering tile at the target zoom — whichever fits the consumer's
+  query pattern).
+- **`Relation`** — resolve member references recursively (members
+  are `Node`/`Way`/`Relation` refs with roles), then centroid /
+  covering tile, or an `admin_level`-boundary walk when the
+  Relation IS an administrative polygon.
+
+The resolved quadkey gets prepended to the per-type OSM ID, yielding
+the `NiblePath` form `osm/<quadkey>/<type>/<id>`. The quadkey IS the
+spatial frame; the per-type ID is the leaf inside it. Three OSM
+Classes (`Node`, `Way`, `Relation`) lift via the queued
+`ogar-from-osm-pbf` adapter (`docs/RDF-OWL-ALIGNMENT.md §10` Phase
+2c). Exercises:
+
+[osm-dm]: https://wiki.openstreetmap.org/wiki/Data_model
 
 - **Spatial prefix-locality** — Cesium TMS quadkey as `NiblePath`
   prefix, per Q2 coordination outcome locked in `lance-graph` PR #473