diff --git a/README.md b/README.md
index 3e8c11c..ef0180f 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ Our objective is to provide a comprehensive, user-friendly weather platform for
 - **Framework**: [SvelteKit](https://kit.svelte.dev/)
 - **Language**: [TypeScript](https://www.typescriptlang.org/)
 - **Data Source**: [Open-Meteo API](https://open-meteo.com/)
-- **Visualization**: [Apache Echarts](https://echarts.apache.org)
+- **Visualization**: custom canvas charts (`src/lib/charts`)
 
 ## Developing
 
@@ -33,3 +33,61 @@ npm run build
 ```
 
 You can preview the production build with `npm run preview`.
+
+## Deployment (static hosting)
+
+The build output in `build/` is a fully static site. Two pieces of server
+configuration are needed:
+
+### 1. SPA fallback
+
+Pages that are not prerendered (unlisted cities, GPS coordinate routes like
+`/weather/week/52.09N5.12E/`) are served by `404.html`, which boots the app
+and resolves the location client-side. Configure the server to serve
+`404.html` for unknown paths.
+
+### 2. Cross-origin isolation (SharedArrayBuffer for the embedded map)
+
+The `/weather/maps/` page embeds `maps.open-meteo.com`, which uses
+`SharedArrayBuffer` for its decoding worker pool. A cross-origin iframe only
+gets `SharedArrayBuffer` when the **embedding** page is cross-origin
+isolated, so this site must be served with:
+
+```
+Cross-Origin-Opener-Policy: same-origin
+Cross-Origin-Embedder-Policy: require-corp
+```
+
+(The map already serves `Cross-Origin-Resource-Policy: cross-origin` and its
+own COOP/COEP, so it is embeddable under these headers. All other assets are
+same-origin and the weather APIs are CORS requests, so `require-corp` is safe
+here.)
+
+### Example: Caddy
+
+```caddy
+ombrella.example.com {
+	root * /srv/ombrella
+	file_server
+	try_files {path} {path}/ /404.html
+	header {
+		Cross-Origin-Opener-Policy "same-origin"
+		Cross-Origin-Embedder-Policy "require-corp"
+	}
+}
+```
+
+### Example: nginx
+
+```nginx
+server {
+	server_name ombrella.example.com;
+	root /srv/ombrella;
+	error_page 404 /404.html;
+	add_header Cross-Origin-Opener-Policy "same-origin" always;
+	add_header Cross-Origin-Embedder-Policy "require-corp" always;
+	location / {
+		try_files $uri $uri/ =404;
+	}
+}
+```
diff --git a/src/lib/components/navigation/weather-nav.svelte b/src/lib/components/navigation/weather-nav.svelte
index b9ec104..392f62b 100644
--- a/src/lib/components/navigation/weather-nav.svelte
+++ b/src/lib/components/navigation/weather-nav.svelte
@@ -135,7 +135,7 @@
 			<div class="flex h-5 w-5 shrink-0 items-center justify-center">
 				<svg
 					class="h-4.5 w-4.5 transition-transform duration-200"
-					class:rotate-180={!collapsed}
+					class:rotate-180={collapsed}
 					fill="none"
 					stroke="currentColor"
 					viewBox="0 0 24 24"
diff --git a/src/routes/weather/maps/+page.svelte b/src/routes/weather/maps/+page.svelte
index d0e06b3..f531954 100644
--- a/src/routes/weather/maps/+page.svelte
+++ b/src/routes/weather/maps/+page.svelte
@@ -1,11 +1,32 @@
 <script lang="ts">
+	import { onMount } from 'svelte';
+
 	import { storedLocation } from '$lib/stores/settings';
 
+	// a #zoom/lat/lng(/bearing/pitch) hash on OUR url is piped through to the
+	// map, so map positions can be bookmarked/shared via ombrella links
+	// (the reverse direction is not possible: the iframe is cross-origin, so
+	// its internal hash changes are unreadable from here)
+	let hashOverride = $state<string | null>(null);
+
+	onMount(() => {
+		const readHash = () => {
+			const hash = window.location.hash;
+			hashOverride = /^#\d+(\.\d+)?\/-?\d+(\.\d+)?\/-?\d+(\.\d+)?/.test(hash) ? hash : null;
+		};
+		readHash();
+		window.addEventListener('hashchange', readHash);
+		return () => window.removeEventListener('hashchange', readHash);
+	});
+
 	// the embedded map understands maplibre's #zoom/lat/lng hash, so the iframe
 	// opens focused on the selected location (zoomed out to regional scale);
 	// picking a new location while on this page recenters the map
 	const iframeSrc = $derived(
-		`https://maps.open-meteo.com/#6/${$storedLocation.latitude.toFixed(3)}/${$storedLocation.longitude.toFixed(3)}`
+		`https://maps.open-meteo.com/${
+			hashOverride ??
+			`#6/${$storedLocation.latitude.toFixed(3)}/${$storedLocation.longitude.toFixed(3)}`
+		}`
 	);
 </script>
 
@@ -18,11 +39,15 @@
 <!-- Full-bleed map: the layout drops its padding for this route. The map
      follows our theme through the color-scheme declared on :root/.dark -->
 <div class="h-full w-full bg-background">
+	<!-- allow="cross-origin-isolated" delegates SharedArrayBuffer use to the
+	     map; it only takes effect when this site itself is served with
+	     COOP/COEP headers (see README, Deployment) -->
 	<iframe
 		src={iframeSrc}
 		title="Open-Meteo Interactive Map"
 		loading="lazy"
 		allowfullscreen
+		allow="cross-origin-isolated"
 		referrerpolicy="no-referrer"
 		class="block h-full w-full border-0"
 		sandbox="allow-scripts allow-same-origin allow-forms allow-popups"