create mvp path

archive/product/data-model/02-geography.md

@@ -0,0 +1,19 @@
+# Domain 2 — Geographic Data
+
+[← Database Model](index.md)
+
+### `provinces` / `cities` / `districts` [CORE]/[MVP]
+**Role:** The geo hierarchy backing service areas, addresses, and search. **Why a table, not a static list:** new cities/districts launch without a deploy, and `sort_order`/`is_active` drive ordered, toggleable dropdowns. `districts` map to Tehran's 22 municipal districts or major neighborhoods elsewhere; they are **optional** (a nurse can cover a whole city). Fields unchanged. **Relations:** `provinces` 1:N `cities` 1:N `districts`; referenced by `customer_addresses` and `nurse_service_areas`.
+
+### `nurse_service_areas` [CORE]
+**Role:** Where a nurse will travel. A row with `district_id = NULL` means the entire city. **Why a join table (not a radius):** Iranian nurses think in named districts, not GPS radii; this also drives the geographic filter in search cheaply. Unchanged, with `UNIQUE(nurse_id, city_id, district_id)`. **Relations:** N:1 → `nurse_profiles`, `cities`, `districts`.
+
+> **As-built (backend-phase-4):** the geo hierarchy lives in a **`geo` schema** (`Provinces`/`Cities`/
+> `Districts`/`NurseServiceAreas`), seeded via `HasData` with all 31 provinces, each province's capital
+> city, and Tehran's 22 مناطق. Because SQL Server treats NULLs as distinct in a unique index, the
+> whole-city (`district_id = NULL`) uniqueness is enforced with a **filtered-index pair** —
+> `UNIQUE(nurse_id, city_id) WHERE district_id IS NULL AND deleted_at IS NULL` **plus**
+> `UNIQUE(nurse_id, city_id, district_id) WHERE district_id IS NOT NULL AND deleted_at IS NULL` — so both a
+> duplicate whole-city row and a duplicate city+district row are rejected (surfaced as `409`), while a
+> soft-removed area can be re-declared. Public lookups are cached and filter `is_active` at every level
+> (a deactivated parent hides its children); geocoding is behind the mocked **`IGeocoder`** seam.