diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -81,5 +81,4 @@ Appen er designet etter «offline-first»-prinsippet:
 
 Kildekoden er lisensiert under [Mozilla Public License 2.0](LICENSE).
 
-Tilfluktsromdata er åpne data fra Geonorge / Direktoratet for samfunnssikkerhet og beredskap (DSB).
-Kartfliser fra OpenStreetMap er lisensiert under [ODbL](https://opendatacommons.org/licenses/odbl/).
+Appen bruker åpne data og tjenester fra flere kilder. Se [SOURCES.md](SOURCES.md) for en fullstendig oversikt over datakilder, URL-er og lisenser.
diff --git a/SOURCES.md b/SOURCES.md
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@@ -0,0 +1,17 @@
+# Data Sources
+
+Centralized list of all external data sources used by the app. This is the authoritative reference for attribution, licensing, and usage context.
+
+## Sources
+
+| Source | Provider | URL | Usage | License | Used in |
+|--------|----------|-----|-------|---------|---------|
+| Shelter data (GeoJSON) | Geonorge / DSB | [nedlasting.geonorge.no/...](https://nedlasting.geonorge.no/geonorge/Samfunnssikkerhet/TilfluktsromOffentlige/GeoJSON/Samfunnssikkerhet_0000_Norge_25833_TilfluktsromOffentlige_GeoJSON.zip) | Shelter locations, capacity, addresses (~556 shelters) | [NLOD 2.0](https://data.norge.no/nlod/no/2.0) | `app/.../data/ShelterRepository.kt`, `pwa/scripts/fetch-shelters.ts` |
+| Map tiles | OpenStreetMap | [tile.openstreetmap.org](https://tile.openstreetmap.org) | Offline-capable map display | [ODbL](https://opendatacommons.org/licenses/odbl/) | `app/` via OSMDroid, `pwa/src/ui/map-view.ts` via Leaflet |
+| Civil defense guidelines | DSB (Direktoratet for samfunnssikkerhet og beredskap) | [dsb.no/sikkerhverdag/egenberedskap](https://www.dsb.no/sikkerhverdag/egenberedskap/) | Emergency instructions shown in the civil defense info dialog | Norwegian public sector information | `app/.../res/values/strings.xml` (civil_defense_* strings) |
+
+## Notes
+
+- **Shelter data** is downloaded as a ZIP containing GeoJSON in EPSG:25833 (UTM33N) projection. The app converts coordinates to WGS84 at parse time.
+- **Map tiles** are cached locally by OSMDroid (Android) and the service worker (PWA) for offline use. OpenStreetMap's [tile usage policy](https://operations.osmfoundation.org/policies/tiles/) applies.
+- **Civil defense guidelines** are adapted from official DSB recommendations, not quoted verbatim. Content is available in English, Bokmal, and Nynorsk.