diff --git a/.env.example b/.env.example
index 26aff1e..ea7f6c2 100644
--- a/.env.example
+++ b/.env.example
@@ -38,3 +38,4 @@ MQTT_SEEN_BROADCAST_MIN_SECONDS=5
 MAP_START_LAT=42.3601
 MAP_START_LON=-71.1500
 MAP_START_ZOOM=10
+MAP_DEFAULT_LAYER=light
diff --git a/README.md b/README.md
index 7f6d7a9..fff3fdb 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,7 @@ Runtime tuning:
 - `ELEVATION_CACHE_TTL` (seconds)
 - `LOS_PEAKS_MAX` (max peaks shown on LOS profile)
 - `MAP_START_LAT` / `MAP_START_LON` / `MAP_START_ZOOM` (default map view)
+- `MAP_DEFAULT_LAYER` (`light`, `dark`, or `topo`; localStorage overrides)
 
 ## Common Commands
 - Rebuild/restart: `docker compose up -d --build`
diff --git a/backend/app.py b/backend/app.py
index 6f76eed..2c5335f 100644
--- a/backend/app.py
+++ b/backend/app.py
@@ -83,6 +83,7 @@ try:
   MAP_START_ZOOM = float(os.getenv("MAP_START_ZOOM", "10"))
 except ValueError:
   MAP_START_ZOOM = 10
+MAP_DEFAULT_LAYER = os.getenv("MAP_DEFAULT_LAYER", "light").strip().lower()
 
 LOS_ELEVATION_URL = os.getenv("LOS_ELEVATION_URL", "https://api.opentopodata.org/v1/srtm90m")
 LOS_SAMPLE_MIN = int(os.getenv("LOS_SAMPLE_MIN", "10"))
@@ -1851,6 +1852,7 @@ def root():
     "MAP_START_LAT": MAP_START_LAT,
     "MAP_START_LON": MAP_START_LON,
     "MAP_START_ZOOM": MAP_START_ZOOM,
+    "MAP_DEFAULT_LAYER": MAP_DEFAULT_LAYER,
     "LOS_ELEVATION_URL": LOS_ELEVATION_URL,
     "LOS_SAMPLE_MIN": LOS_SAMPLE_MIN,
     "LOS_SAMPLE_MAX": LOS_SAMPLE_MAX,
diff --git a/backend/static/index.html b/backend/static/index.html
index e7748b9..e3d28bf 100644
--- a/backend/static/index.html
+++ b/backend/static/index.html
@@ -444,7 +444,10 @@
       maxZoom: 17,
       attribution: '© OpenStreetMap contributors © OpenTopoMap'
     });
-    let baseLayer = 'light';
+    let baseLayer = '{{MAP_DEFAULT_LAYER}}';
+    if (baseLayer !== 'dark' && baseLayer !== 'topo' && baseLayer !== 'light') {
+      baseLayer = 'light';
+    }
     const storedLayer = localStorage.getItem('meshmapBaseLayer');
     if (storedLayer === 'dark' || storedLayer === 'topo' || storedLayer === 'light') {
       baseLayer = storedLayer;
diff --git a/docker-compose.yaml b/docker-compose.yaml
index ae54787..9e6d084 100644
--- a/docker-compose.yaml
+++ b/docker-compose.yaml
@@ -34,6 +34,7 @@ services:
       MAP_START_LAT: "${MAP_START_LAT:-42.3601}"
       MAP_START_LON: "${MAP_START_LON:--71.1500}"
       MAP_START_ZOOM: "${MAP_START_ZOOM:-10}"
+      MAP_DEFAULT_LAYER: "${MAP_DEFAULT_LAYER:-light}"
     restart: unless-stopped
     volumes:
       - ./data:/data
diff --git a/docs.md b/docs.md
index ef9ec24..f8e7630 100644
--- a/docs.md
+++ b/docs.md
@@ -31,6 +31,7 @@ This project renders live MeshCore traffic on a Leaflet + OpenStreetMap map. A F
 - Legend is collapsible and persisted to localStorage.
 - HUD is capped to `90vh` and scrolls to avoid running off-screen.
 - Map start position is configurable with `MAP_START_LAT`, `MAP_START_LON`, `MAP_START_ZOOM`.
+- Default base layer can be set with `MAP_DEFAULT_LAYER` (localStorage overrides).
 - Node search (name or key) and a labels toggle (persisted to localStorage).
 - Hide Nodes toggle hides markers and trails; routes remain visible.
 - Propagation overlay keeps heat/routes/trails/markers above it after render.