Split offline hiking trails per country, add a picker instead of one big file

data/hiking_trails.geojson is now data/hiking_trails/<CODE>.geojson —
one file per country instead of a merge, generated per-source
(PmtilesBuilder.extract_hiking_trails), cached the same way
geofabrik_cache is (skipped once a country's own extract is already
newer than its source .osm.pbf, so growing the selection by one
country only re-extracts that one). GET /api/hiking-trails now lists
available country codes instead of a single file's status.

The Overlays panel's "Hiking trails" item becomes an expandable
per-country checklist once any offline extract exists (same shape as
Radar's own expand), replacing the plain on/off checkbox — nobody
covering a dozen countries' worth of offline map data needs all of
their hiking trails loaded and parsed at once, so each ticked country
fetches its own GeoJSON independently instead.

HikingTrails.extract_merged (server-side multi-country merge, no
longer needed now that the client picks per country) removed again.
Verified the new extract_hiking_trails + caching skip live on brick
against a real cached country PBF.

TODO.adoc

@@ -13,8 +13,7 @@ independence from connectivity.
 ** [ ] Terrain slope readout for parking (numeric, not just visual shading)
 * [ ] Contour lines from OSM for hikes and mountain passes
 * [x] Hiking trail overlay — Waymarked Trails raster tiles online (`public/js/hiking_trails.js`), colored per-route by the OSM `colour` tag they already render (the KST/KČT paint-blaze colors in Slovakia/Czechia, plain red elsewhere). Click queries a one-off Overpass `around` search (racing 3 public mirrors) for the route's name/colour/network/operator/distance
-** [x] Offline copy wired in for real, no custom Planetiler profile needed — `Maptool::HikingTrails` (`lib/maptool/hiking_trails.rb`) runs `osmium tags-filter r/route=hiking` + `add-locations-to-ways` + `cat -f opl` against the *same* per-country Geofabrik `.osm.pbf` already downloaded for `offline.pmtiles`, no new download. Generated automatically as the last step of every offline build (`PmtilesBuilder.extract_hiking_trails`, best-effort — a failure here doesn't fail the whole build) into `data/hiking_trails.geojson`, served at `GET /tiles/hiking_trails.geojson` only once the overlay's actually toggled on. Offline click uses a local `queryRenderedFeatures` hit-test instead of Overpass — instant, no network. See docs/development.adoc
-*** [ ] File size for a many-country selection could get large (Slovakia alone: ~3000 routes) — coordinates are rounded to 5dp but there's no real tiling/simplification yet; revisit if a big selection makes the browser fetch noticeably slow
+** [x] Offline copy wired in for real, no custom Planetiler profile needed — `Maptool::HikingTrails` (`lib/maptool/hiking_trails.rb`) runs `osmium tags-filter r/route=hiking` + `add-locations-to-ways` + `cat -f opl` against the *same* per-country Geofabrik `.osm.pbf` already downloaded for `offline.pmtiles`, no new download. One `data/hiking_trails/<CODE>.geojson` per country (not one combined file), generated as the last step of every offline build and cached like `geofabrik_cache` (skipped once already newer than its source PBF) — a many-country selection no longer means one giant file, since `GET /api/hiking-trails` lists available countries and the Overlays panel's own checklist only fetches `GET /tiles/hiking_trails/<CODE>.geojson` for whichever ones get ticked. Offline click uses a local `queryRenderedFeatures` hit-test instead of Overpass — instant, no network. See docs/development.adoc
 * [x] Overpass/OSM scripts to extract POIs (drinking water, dump stations, LPG, public toilets, laundromats, shops, springs) — `rake overpass:pois`, see docs/development.adoc; writes a `.geojson` to drop in `data/gpx/` or upload. Also runnable from inside the app itself now, see the import plugins entry below (`plugins/overpass-pois` wraps this same query). Each category now carries a real `POI_ICONS` glyph and color (not p4n2gpx's plain red marker) plus a popup description built from opening_hours/operator/website tags
 * [x] Import plugins: a pluggable way to add more data sources (Park4Night, iOverlander, Freecampsites, ...) without their scrapers necessarily living in this (public) repo — sidebar icon (logged in only) lists whatever's under `plugins/`, "Run for this area" uses the current map viewport as the bbox, no separate area-picker needed. Contract: a `plugin.json` manifest + a script that reads `--south`/`--west`/`--north`/`--east` and prints a GeoJSON `FeatureCollection` to stdout (`lib/maptool/plugins.rb`, `GET /api/plugins`, `POST /api/plugins/:name/run`) — output saved the same way an upload would be. `plugins/overpass-pois` ships as the reference example; a private/ToS-sensitive scraper just drops its own directory in locally and is never `git add`ed
 ** [x] Park4Night — private plugin (`data/plugins/p4n2gpx/`, outside this repo per the "ToS-sensitive scraper" note above); iOverlander/Freecampsites still open, same story

app.rb

@@ -62,7 +62,6 @@ module Maptool
 
     OFFLINE_PMTILES_PATH = File.join(DATA_DIR, "offline.pmtiles")
     TERRAIN_PMTILES_PATH = File.join(DATA_DIR, "terrain.pmtiles")
-    HIKING_TRAILS_PATH = PmtilesBuilder.hiking_trails_path(DATA_DIR)
     GPX_STORE = GpxStore.new(File.join(DATA_DIR, "gpx"))
     LIVETRACK_STORE = LiveTrackStore.new(File.join(DATA_DIR, "livetrack.json"))
 
@@ -361,24 +360,28 @@ module Maptool
     # PmtilesBuilder.extract_hiking_trails) rather than its own separate
     # build — it's derived from the exact same per-country .osm.pbf cache
     # offline.pmtiles itself already downloads, so there's nothing of its
-    # own to trigger or delete; DELETE /api/offline-tiles removes this
-    # file too. No `meta` argument here (unlike offline/terrain above) —
-    # parsing the whole GeoJSON just to report a feature count would cost
-    # real time on every page load's status check for what's a multi-MB
-    # file across several countries; size/mtime alone is enough to know
-    # whether it's there.
+    # own to trigger; DELETE /api/offline-tiles removes it too. One file
+    # per country (not one combined file) so a viewer only ever fetches
+    # the country they actually pick in the Hiking trails overlay's own
+    # checklist (public/js/hiking_trails.js), not every selected country's
+    # trails at once — `countries` lists which ones exist to build that
+    # checklist from.
     get "/api/hiking-trails" do
-      json pmtiles_file_status(HIKING_TRAILS_PATH, nil)
+      json countries: PmtilesBuilder.hiking_trails_countries(DATA_DIR)
     end
 
-    # Fetched client-side only when the Hiking trails overlay is actually
-    # toggled on (public/js/hiking_trails.js), not on page load — same
-    # "on demand" story as the online raster tiles it replaces once this
-    # is available.
-    get "/tiles/hiking_trails.geojson" do
-      halt 404 unless File.exist?(HIKING_TRAILS_PATH)
+    # Fetched client-side only for a country the viewer actually ticks in
+    # the Hiking trails checklist, not on page load. :code is constrained
+    # to exactly what hiking_trails_countries can ever return (two
+    # uppercase letters) — otherwise this would accept an arbitrary
+    # ".."-laden path segment.
+    get "/tiles/hiking_trails/:code.geojson" do
+      halt 404 unless params[:code].match?(/\A[A-Z]{2}\z/)
 
-      send_file HIKING_TRAILS_PATH, type: "application/geo+json"
+      path = PmtilesBuilder.hiking_trails_country_path(DATA_DIR, params[:code])
+      halt 404 unless File.exist?(path)
+
+      send_file path, type: "application/geo+json"
     end
 
     # Pinged once per page load (public/js/map.js) — url is a same-origin

docs/development.adoc

@@ -106,11 +106,12 @@ size rather than assuming one, so this isn't a problem either way.
 The sidebar's "Hiking trails" overlay works online out of the box
 (waymarkedtrails.org raster tiles, `public/js/hiking_trails.js`) —
 clicking a trail fires a one-off Overpass query for its name/colour/
-network/distance. For it to work offline too, `data/hiking_trails.geojson`
-is generated automatically as the last step of every `offline.pmtiles`
-build (`Maptool::HikingTrails`, `lib/maptool/hiking_trails.rb`), straight
-from the *same* per-country `.osm.pbf` files already downloaded for
-`offline.pmtiles` itself — no separate download, no third-party service:
+network/distance. For it to work offline too, one `data/hiking_trails/
+<CODE>.geojson` per country is generated automatically as the last step
+of every `offline.pmtiles` build (`Maptool::HikingTrails`,
+`lib/maptool/hiking_trails.rb`), straight from the *same* per-country
+`.osm.pbf` files already downloaded for `offline.pmtiles` itself — no
+separate download, no third-party service:
 
 [source,shell]
 ----
@@ -130,20 +131,30 @@ tool stitches a route relation's member ways into one line for you
 waymarkedtrails.org and this app's own online Overpass click handler
 already do.
 
-Best-effort: a hiking-trails extraction problem on one country's PBF
-logs a warning and is skipped rather than failing the whole
-`offline.pmtiles` build over what's a bonus overlay, not the core map
-(`PmtilesBuilder.extract_hiking_trails`). Coordinates are rounded to 5
-decimal places (~1m, plenty for a rendered line) to keep the combined
-file smaller — for a many-country selection it can still be a sizeable
-GeoJSON (Slovakia alone: ~3000 routes, ~30MB unrounded), fetched
-client-side only once the overlay is actually toggled on, not on page
-load. `rake hiking:trails[pbf,out]` runs the extraction by hand against
-one `.osm.pbf` for testing.
+Best-effort per country: an extraction problem on one country's PBF logs
+a warning and is skipped rather than failing the whole `offline.pmtiles`
+build, or even the other countries in the same selection, over what's a
+bonus overlay, not the core map (`PmtilesBuilder.extract_hiking_trails`).
+Cached the same way `geofabrik_cache` is (skipped once a country's own
+extract is already newer than its source `.osm.pbf`), so growing the
+region selection by one country only extracts that one. Coordinates are
+rounded to 5 decimal places (~1m, plenty for a rendered line) — Slovakia
+alone is ~3000 routes, ~30MB unrounded.
 
-`DELETE /api/offline-tiles` removes this file along with `offline.pmtiles`
-and the Geofabrik cache — there's no separate delete/rebuild route for it,
-since it's not an independent build.
+One file per country rather than one combined file: `GET /api/hiking-trails`
+lists which country codes have an extract (`countries: [...]`), and the
+Overlays panel's "Hiking trails" item turns that into a checklist —
+each ticked country fetches its own `GET /tiles/hiking_trails/<CODE>.geojson`
+only then, not on page load and not for countries never ticked. Offline
+click hit-tests the loaded vector layer(s) directly
+(`queryRenderedFeatures`) instead of querying Overpass, so it resolves
+instantly with no network at all. `rake hiking:trails[pbf,out]` runs the
+extraction by hand against one `.osm.pbf` for testing.
+
+`DELETE /api/offline-tiles` removes the whole `data/hiking_trails/`
+directory along with `offline.pmtiles` and the Geofabrik cache — there's
+no separate delete/rebuild route for it, since it's not an independent
+build.
 
 == In-app regeneration
 

lib/maptool/hiking_trails.rb

@@ -63,22 +63,6 @@ module Maptool
       end
     end
 
-    # Runs extract() over one .osm.pbf per selected country and combines the
-    # results into a single FeatureCollection — a route relation crossing a
-    # border (an E-path, say) shows up once per country whose extract it
-    # was pulled from, deduplicated here by OSM relation id (properties.id)
-    # rather than left to render as overlapping duplicate lines.
-    # extract: same injectable-seam reasoning as PmtilesBuilder's own
-    # download_extract:/fetch_manifest: — lets a test swap out the real
-    # (osmium-shelling-out) implementation for a canned one.
-    def self.extract_merged(pbf_paths, extract: method(:extract))
-      seen = {}
-      pbf_paths.each do |pbf_path|
-        extract.call(pbf_path)["features"].each { |feature| seen[feature["properties"]["id"]] ||= feature }
-      end
-      { "type" => "FeatureCollection", "features" => seen.values }
-    end
-
     # Pure — no subprocess — so it's cheaply testable against a canned OPL
     # fixture, same "keep the real logic testable without the real tool
     # installed" reasoning OverpassPois.to_geojson already gives for staying

lib/maptool/pmtiles_builder.rb

@@ -299,26 +299,55 @@ module Maptool
     end
     private_class_method :extract_offline
 
-    # Runs over the same per-country .osm.pbf files sources above already
+    # One GeoJSON per country (data/hiking_trails/<CODE>.geojson), not one
+    # merged file — the frontend only ever needs to show a country at a
+    # time the viewer actually picks (see HikingTrailsControl's country
+    # checklist), and a combined multi-country file was needlessly making
+    # every viewer fetch every selected country's trails regardless.
+    #
+    # Runs over the same per-country .osm.pbf files `sources` above already
     # downloaded/cached for offline.pmtiles itself — no separate download.
-    # Best-effort: a hiking-trails extraction problem (a malformed PBF
-    # region, osmium hiccup on one particular file) shouldn't fail the
-    # whole offline.pmtiles build over what's a bonus overlay, not the
-    # core map — logged into the sidecar meta's own "error" field instead,
-    # so it's visible without taking build_offline itself down.
+    # Cached the same way geofabrik_cache is: skipped for a country whose
+    # extract is already newer than its source .osm.pbf, so growing the
+    # region selection by one country only extracts that one, not every
+    # already-covered country all over again.
+    #
+    # Best-effort per country: an extraction problem (a malformed PBF
+    # region, an osmium hiccup) shouldn't fail the whole offline.pmtiles
+    # build, or even the other countries in this same selection, over
+    # what's a bonus overlay, not the core map.
     def self.extract_hiking_trails(sources, data_dir)
-      geojson = HikingTrails.extract_merged(sources.map { |s| s["path"] })
-      tmp_path = "#{hiking_trails_path(data_dir)}.tmp"
-      File.write(tmp_path, JSON.generate(geojson))
-      File.rename(tmp_path, hiking_trails_path(data_dir))
-    rescue HikingTrails::ExtractError => e
-      File.delete(tmp_path) if tmp_path && File.exist?(tmp_path)
-      warn "hiking trails extraction failed, skipping: #{e.message}"
+      FileUtils.mkdir_p(hiking_trails_dir(data_dir))
+      sources.each do |source|
+        out_path = hiking_trails_country_path(data_dir, source["code"])
+        next if File.exist?(out_path) && File.mtime(out_path) >= File.mtime(source["path"])
+
+        tmp_path = "#{out_path}.tmp"
+        begin
+          File.write(tmp_path, JSON.generate(HikingTrails.extract(source["path"])))
+          File.rename(tmp_path, out_path)
+        rescue HikingTrails::ExtractError => e
+          File.delete(tmp_path) if File.exist?(tmp_path)
+          warn "hiking trails extraction failed for #{source["code"]}, skipping: #{e.message}"
+        end
+      end
     end
     private_class_method :extract_hiking_trails
 
-    def self.hiking_trails_path(data_dir)
-      File.join(data_dir, "hiking_trails.geojson")
+    def self.hiking_trails_dir(data_dir)
+      File.join(data_dir, "hiking_trails")
+    end
+
+    def self.hiking_trails_country_path(data_dir, code)
+      File.join(hiking_trails_dir(data_dir), "#{code}.geojson")
+    end
+
+    # Country codes with an already-extracted offline hiking-trails file,
+    # sorted — not necessarily the same as the *current* region selection
+    # (accumulates like geofabrik_cache does; a country deselected after
+    # being built once is left alone rather than swept up here).
+    def self.hiking_trails_countries(data_dir)
+      Dir.glob(File.join(hiking_trails_dir(data_dir), "*.geojson")).map { |path| File.basename(path, ".geojson") }.sort
     end
 
     # Renders a report_step string like "fetching PL (3/4) — done: SK, CZ —
@@ -468,7 +497,7 @@ module Maptool
 
       File.delete(File.join(data_dir, "offline.pmtiles")) if File.exist?(File.join(data_dir, "offline.pmtiles"))
       File.delete(offline_meta_path(data_dir)) if File.exist?(offline_meta_path(data_dir))
-      File.delete(hiking_trails_path(data_dir)) if File.exist?(hiking_trails_path(data_dir))
+      FileUtils.remove_entry(hiking_trails_dir(data_dir)) if Dir.exist?(hiking_trails_dir(data_dir))
       cache_dir = geofabrik_cache_dir(data_dir)
       FileUtils.remove_entry(cache_dir) if Dir.exist?(cache_dir)
     end

public/css/style.css

@@ -1579,6 +1579,22 @@ html, body {
   font-size: 12px;
 }
 
+.hiking-trail-countries {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 4px 12px;
+  list-style: none;
+  margin: 0;
+  padding: 0;
+}
+
+.hiking-trail-countries__item label {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  cursor: pointer;
+}
+
 .livetrack-panel__list {
   flex: 1;
   overflow-y: auto;

public/js/hiking_trails.js

@@ -4,9 +4,6 @@ import { firstSymbolLayerId } from "/js/radar.js";
 import { escapeHtml } from "/js/gpx.js";
 import { lineLength, formatDistance } from "/js/measure.js";
 
-const SOURCE_ID = "hiking-trails";
-const LAYER_ID = "hiking-trails-line";
-
 // Overpass has permissive CORS (verified: Access-Control-Allow-Origin: *),
 // so this queries it directly from the browser — no server-side proxy
 // needed, same "public API, no key" story as the Nominatim search already
@@ -34,22 +31,36 @@ const SAFE_COLOR = /^(#[0-9a-fA-F]{3,8}|[a-zA-Z]+)$/;
 // Pre-rendered raster tiles, not vector — waymarkedtrails.org already
 // colors each route by its OSM `colour` tag (the KST/KČT-style paint-blaze
 // colors used in Slovakia/Czechia), falling back to plain red where a route
-// has none, so there's no styling to do here ourselves. Used when there's
-// no local offline extraction to draw from instead (see _addOfflineLayer
-// below) — same "quietly renders nothing without a network" story as the
-// Wikipedia/Radar/Contour lines overlays.
+// has none, so there's no styling to do here ourselves. Used whenever no
+// offline extract is available at all — same "quietly renders nothing
+// without a network" story as the Wikipedia/Radar/Contour lines overlays.
+const ONLINE_SOURCE_ID = "hiking-trails-online";
+const ONLINE_LAYER_ID = "hiking-trails-online-line";
 const TILE_URL = "https://tile.waymarkedtrails.org/hiking/{z}/{x}/{y}.png";
 const ATTRIBUTION =
   'Trails &copy; <a href="https://waymarkedtrails.org" target="_blank">Waymarked Trails</a> (CC-BY-SA), map data &copy; OpenStreetMap contributors';
 const OPACITY = 0.85;
 
-// Offline: a real vector line layer, GeoJSON generated at build time by
-// Maptool::HikingTrails straight from the same Geofabrik .osm.pbf
-// offline.pmtiles itself is built from (see lib/maptool/hiking_trails.rb,
-// PmtilesBuilder.extract_offline) — no network needed at all, and no
-// waiting on Overpass for click details either (queried locally via
-// queryRenderedFeatures instead, see _handleClick below).
-const OFFLINE_GEOJSON_URL = "/tiles/hiking_trails.geojson";
+// Offline: one real vector line layer per country the viewer actually
+// picks, GeoJSON generated at build time by Maptool::HikingTrails straight
+// from the same Geofabrik .osm.pbf offline.pmtiles itself is built from
+// (see lib/maptool/hiking_trails.rb, PmtilesBuilder.extract_hiking_trails)
+// — no network needed, and no waiting on Overpass for click details either
+// (queried locally via queryRenderedFeatures instead, see _handleClick
+// below). One file per country rather than one combined file: a viewer
+// covering a dozen countries' worth of offline map data rarely wants all
+// of their hiking trails loaded at once, so this is opt-in per country
+// instead.
+function offlineSourceId(code) {
+  return `hiking-trails-offline-${code}`;
+}
+function offlineLayerId(code) {
+  return `hiking-trails-offline-${code}-line`;
+}
+function offlineUrl(code) {
+  return `/tiles/hiking_trails/${code}.geojson`;
+}
+
 // waymarkedtrails.org's own fallback for an untagged route.
 const DEFAULT_TRAIL_COLOR = "#c1272d";
 // Real-world `colour` values seen in production data (see the 2026-09-13
@@ -66,68 +77,115 @@ function normalizedTrailColor(raw) {
   return /^#[0-9a-fA-F]{3,8}$/.test(trimmed) ? trimmed : DEFAULT_TRAIL_COLOR;
 }
 
-// A plain on/off Overlays item, same shape as ContourControl — one static
-// raster overlay, no scrub/forecast controls to expand into.
+// An Overlays panel item — a plain on/off checkbox (raster overlay) until
+// offline extracts exist for at least one country, at which point it
+// becomes an expandable per-country checklist instead (same expand shape
+// as RadarControl), since a viewer with a dozen countries' worth of
+// offline map data rarely wants all of their hiking trails loaded, let
+// alone parsed by the browser, at once.
 export class HikingTrailsControl {
   constructor(map) {
     this._map = map;
-    this._active = false;
-    this._offlineAvailable = false;
-    this._clickHandler = (event) => this._handleClick(event);
+    this._active = false; // the online-mode checkbox's own state
+    this._offlineCountries = []; // codes with an extract available on the server
+    this._selectedCountries = new Set(); // codes currently shown, offline mode
+
+    map.on("click", (event) => this._handleClick(event));
 
     // setStyle() (switching Online/Offline) tears down all custom sources/
-    // layers — put this back if it was on, same as every other Overlays
-    // control.
+    // layers — put whatever was showing back, same as every other
+    // Overlays control.
     map.on("style.load", () => {
-      if (this._active) this._addLayer();
+      if (this._active) this._addOnlineLayer();
+      for (const code of this._selectedCountries) this._addOfflineLayer(code);
     });
   }
 
-  // Called once map.js's GET /api/hiking-trails check resolves — same
-  // "prefer the local file whenever it exists" story as
-  // OverlaysControl#setHillshadeOfflineAvailable, independent of whether
-  // the Online or Offline *base map* happens to be selected right now.
-  setOfflineAvailable(available) {
-    this._offlineAvailable = available;
-  }
-
   mount(li) {
     li.innerHTML = `
-      <label>
+      <div class="overlays-panel__row">
         <input type="checkbox" class="overlays-panel__toggle">
         <span class="overlays-panel__icon">${WALKING_ICON}</span>
-        <span>Hiking trails</span>
-      </label>
+        <button type="button" class="overlays-panel__name">Hiking trails</button>
+      </div>
+      <div class="overlays-panel__details" hidden>
+        <ul class="hiking-trail-countries"></ul>
+      </div>
     `;
     this._checkbox = li.querySelector(".overlays-panel__toggle");
-    this._checkbox.addEventListener("change", (event) => this._toggle(event.target.checked));
+    this._nameButton = li.querySelector(".overlays-panel__name");
+    this._details = li.querySelector(".overlays-panel__details");
+    this._countryList = li.querySelector(".hiking-trail-countries");
+
+    this._checkbox.addEventListener("change", (event) => this._toggleOnline(event.target.checked));
+    this._nameButton.addEventListener("click", () => {
+      if (this._offlineCountries.length === 0) return; // nothing to expand into yet
+      const expanding = this._details.hidden;
+      this._details.hidden = !expanding;
+      this._nameButton.setAttribute("aria-expanded", String(expanding));
+    });
   }
 
-  _toggle(active) {
+  // Called once map.js's GET /api/hiking-trails check resolves. Switches
+  // this item from "online raster, plain on/off" to "offline vector,
+  // pick your countries" — the two are mutually exclusive rather than
+  // both offered at once, since once a real local extract exists there's
+  // no reason to still fall back to a third-party tile server for any of
+  // it.
+  setOfflineCountries(countries) {
+    this._offlineCountries = countries;
+    if (countries.length === 0) return;
+
+    if (this._active) this._toggleOnline(false);
+    this._checkbox.hidden = true;
+
+    this._countryList.innerHTML = countries
+      .map(
+        (code) => `
+          <li class="hiking-trail-countries__item">
+            <label>
+              <input type="checkbox" class="hiking-trail-countries__toggle" value="${code}">
+              ${code}
+            </label>
+          </li>
+        `,
+      )
+      .join("");
+    this._countryList.querySelectorAll(".hiking-trail-countries__toggle").forEach((input) => {
+      input.addEventListener("change", (event) => this._toggleCountry(event.target.value, event.target.checked));
+    });
+  }
+
+  _toggleOnline(active) {
     this._active = active;
+    if (active) this._addOnlineLayer();
+    else this._removeOnlineLayer();
+  }
+
+  _toggleCountry(code, active) {
     if (active) {
-      this._addLayer();
-      this._map.on("click", this._clickHandler);
+      this._selectedCountries.add(code);
+      this._addOfflineLayer(code);
     } else {
-      this._removeLayer();
-      this._map.off("click", this._clickHandler);
+      this._selectedCountries.delete(code);
+      this._removeOfflineLayer(code);
     }
   }
 
   _handleClick(event) {
-    if (this._offlineAvailable) {
-      this._handleOfflineClick(event);
-    } else {
-      this._handleOnlineClick(event);
-    }
+    if (this._selectedCountries.size > 0) this._handleOfflineClick(event);
+    else if (this._active) this._handleOnlineClick(event);
   }
 
-  // The local vector layer has real features to hit-test directly — no
+  // The local vector layers have real features to hit-test directly — no
   // network round-trip, so this resolves instantly. A genuine miss (empty
   // result) shows no popup at all rather than a "not found" message, same
   // as clicking empty space anywhere else on the map.
   _handleOfflineClick(event) {
-    const features = this._map.queryRenderedFeatures(event.point, { layers: [LAYER_ID] });
+    const layers = [...this._selectedCountries].map(offlineLayerId).filter((id) => this._map.getLayer(id));
+    if (layers.length === 0) return;
+
+    const features = this._map.queryRenderedFeatures(event.point, { layers });
     if (features.length === 0) return;
 
     const seen = new Set();
@@ -165,45 +223,10 @@ export class HikingTrailsControl {
     );
   }
 
-  async _addLayer() {
-    if (this._map.getSource(SOURCE_ID)) return;
-
-    if (this._offlineAvailable) await this._addOfflineLayer();
-    else this._addOnlineLayer();
-  }
-
-  async _addOfflineLayer() {
-    let geojson;
-    try {
-      geojson = await (await fetch(OFFLINE_GEOJSON_URL)).json();
-    } catch {
-      return; // degrade quietly, same story as every other optional layer here
-    }
-    if (this._map.getSource(SOURCE_ID)) return; // toggled off and back on again while this was fetching
-
-    // Normalized once here (rather than a MapLibre expression in the paint
-    // property below) so an untrustworthy `colour` tag value never reaches
-    // a style property directly — same reasoning gpx.js's own
-    // feature.properties.color ||= TRACK_COLOR normalization gives.
-    for (const feature of geojson.features) {
-      feature.properties.color = normalizedTrailColor(feature.properties.colour);
-    }
-
-    this._map.addSource(SOURCE_ID, { type: "geojson", data: geojson });
-    this._map.addLayer(
-      {
-        id: LAYER_ID,
-        type: "line",
-        source: SOURCE_ID,
-        layout: { "line-cap": "round", "line-join": "round" },
-        paint: { "line-color": ["get", "color"], "line-width": 2 },
-      },
-      firstSymbolLayerId(this._map),
-    );
-  }
-
   _addOnlineLayer() {
-    this._map.addSource(SOURCE_ID, {
+    if (this._map.getSource(ONLINE_SOURCE_ID)) return;
+
+    this._map.addSource(ONLINE_SOURCE_ID, {
       type: "raster",
       tiles: [TILE_URL],
       tileSize: 256,
@@ -213,14 +236,52 @@ export class HikingTrailsControl {
     // Below labels (same firstSymbolLayerId spot contour.js/radar.js use),
     // so place names/POI icons stay readable on top of the trail lines.
     this._map.addLayer(
-      { id: LAYER_ID, type: "raster", source: SOURCE_ID, paint: { "raster-opacity": OPACITY } },
+      { id: ONLINE_LAYER_ID, type: "raster", source: ONLINE_SOURCE_ID, paint: { "raster-opacity": OPACITY } },
       firstSymbolLayerId(this._map),
     );
   }
 
-  _removeLayer() {
-    if (this._map.getLayer(LAYER_ID)) this._map.removeLayer(LAYER_ID);
-    if (this._map.getSource(SOURCE_ID)) this._map.removeSource(SOURCE_ID);
+  _removeOnlineLayer() {
+    if (this._map.getLayer(ONLINE_LAYER_ID)) this._map.removeLayer(ONLINE_LAYER_ID);
+    if (this._map.getSource(ONLINE_SOURCE_ID)) this._map.removeSource(ONLINE_SOURCE_ID);
+  }
+
+  async _addOfflineLayer(code) {
+    if (this._map.getSource(offlineSourceId(code))) return;
+
+    let geojson;
+    try {
+      geojson = await (await fetch(offlineUrl(code))).json();
+    } catch {
+      return; // degrade quietly, same story as every other optional layer here
+    }
+    // Toggled back off, or the base map switched, while this was fetching.
+    if (!this._selectedCountries.has(code) || this._map.getSource(offlineSourceId(code))) return;
+
+    // Normalized once here (rather than a MapLibre expression in the paint
+    // property below) so an untrustworthy `colour` tag value never reaches
+    // a style property directly — same reasoning gpx.js's own
+    // feature.properties.color ||= TRACK_COLOR normalization gives.
+    for (const feature of geojson.features) {
+      feature.properties.color = normalizedTrailColor(feature.properties.colour);
+    }
+
+    this._map.addSource(offlineSourceId(code), { type: "geojson", data: geojson });
+    this._map.addLayer(
+      {
+        id: offlineLayerId(code),
+        type: "line",
+        source: offlineSourceId(code),
+        layout: { "line-cap": "round", "line-join": "round" },
+        paint: { "line-color": ["get", "color"], "line-width": 2 },
+      },
+      firstSymbolLayerId(this._map),
+    );
+  }
+
+  _removeOfflineLayer(code) {
+    if (this._map.getLayer(offlineLayerId(code))) this._map.removeLayer(offlineLayerId(code));
+    if (this._map.getSource(offlineSourceId(code))) this._map.removeSource(offlineSourceId(code));
   }
 }
 

public/js/map.js

@@ -609,7 +609,7 @@ fetch("/api/terrain-tiles")
 
 fetch("/api/hiking-trails")
   .then((response) => response.json())
-  .then(({ available }) => overlaysControl.setHikingTrailsOfflineAvailable(available))
+  .then(({ countries }) => overlaysControl.setHikingTrailsOfflineCountries(countries))
   .catch(() => {});
 
 fetch("/api/kiwix")

public/js/overlays.js

@@ -219,7 +219,7 @@ export class OverlaysControl {
       <li class="overlays-panel__item overlays-panel__item--expandable"></li>
       <li class="overlays-panel__item overlays-panel__item--expandable"></li>
       <li class="overlays-panel__item"></li>
-      <li class="overlays-panel__item"></li>
+      <li class="overlays-panel__item overlays-panel__item--expandable"></li>
     `;
     const [hillshadeItem, wikiItem, radarItem, shadowItem, contourItem, hikingTrailsItem] = list.children;
     this._hillshade.mount(hillshadeItem);
@@ -245,8 +245,8 @@ export class OverlaysControl {
     this._hillshade.setOfflineAvailable(available);
   }
 
-  setHikingTrailsOfflineAvailable(available) {
-    this._hikingTrails.setOfflineAvailable(available);
+  setHikingTrailsOfflineCountries(countries) {
+    this._hikingTrails.setOfflineCountries(countries);
   }
 
   // Called by map.js's PitchToggleControl whenever the 3D pitch toggle

test/test_app.rb

@@ -39,13 +39,17 @@ class AppTest < Minitest::Test
     assert_equal({ "available" => false }, json_body(response))
   end
 
-  def test_hiking_trails_reports_unavailable_when_no_geojson_present
+  def test_hiking_trails_reports_no_countries_when_none_extracted_yet
     response = request.get("/api/hiking-trails")
-    assert_equal({ "available" => false }, json_body(response))
+    assert_equal({ "countries" => [] }, json_body(response))
   end
 
-  def test_hiking_trails_file_404s_when_no_geojson_present
-    assert_equal 404, request.get("/tiles/hiking_trails.geojson").status
+  def test_hiking_trails_file_404s_for_a_country_with_no_extract
+    assert_equal 404, request.get("/tiles/hiking_trails/SK.geojson").status
+  end
+
+  def test_hiking_trails_file_404s_for_a_malformed_country_code
+    assert_equal 404, request.get("/tiles/hiking_trails/../../etc/passwd.geojson").status
   end
 
   def test_kiwix_reports_unavailable_when_no_url_configured

test/test_hiking_trails.rb

@@ -111,21 +111,6 @@ class HikingTrailsTest < Minitest::Test
     assert_equal [[[20.08765, 49.17912], [20.088, 49.18]]], coords
   end
 
-  def test_extract_merged_deduplicates_by_relation_id_across_files
-    feature = ->(id) {
-      { "type" => "Feature", "properties" => { "id" => id, "name" => "Trail #{id}" }, "geometry" => { "type" => "MultiLineString", "coordinates" => [] } }
-    }
-    # Relation 1 shows up in both "country" files (a cross-border trail);
-    # relation 2 only in the second.
-    per_file = { "at.osm.pbf" => [feature.call(1)], "cz.osm.pbf" => [feature.call(1), feature.call(2)] }
-    extract = ->(pbf_path) { { "type" => "FeatureCollection", "features" => per_file.fetch(pbf_path) } }
-
-    merged = Maptool::HikingTrails.extract_merged(%w[at.osm.pbf cz.osm.pbf], extract: extract)
-    ids = merged["features"].map { |f| f["properties"]["id"] }.sort
-
-    assert_equal [1, 2], ids
-  end
-
   def test_parse_opl_ignores_a_dangling_member_reference_but_keeps_the_rest
     opl = <<~OPL
       w1 Thighway=path Nn10x20.087y49.179,n11x20.088y49.18

test/test_pmtiles_builder.rb

@@ -216,20 +216,44 @@ class PmtilesBuilderTest < Minitest::Test
     )
   end
 
-  def test_build_offline_also_writes_a_hiking_trails_geojson
+  def test_build_offline_also_writes_a_per_country_hiking_trails_geojson
     select_regions("SK")
     thread = Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download)
     thread.join
 
     # The fake osmium binary doesn't produce real OPL output, just
-    # confirms the file lands and is valid (empty) GeoJSON — the real
-    # parsing logic is covered by test_hiking_trails.rb against real OPL
-    # fixtures.
-    path = File.join(@data_dir, "hiking_trails.geojson")
-    assert_path_exists path
+    # confirms the file lands (one per country) and is valid (empty)
+    # GeoJSON — the real parsing logic is covered by test_hiking_trails.rb
+    # against real OPL fixtures.
+    assert_equal ["SK"], Maptool::PmtilesBuilder.hiking_trails_countries(@data_dir)
+    path = Maptool::PmtilesBuilder.hiking_trails_country_path(@data_dir, "SK")
     assert_equal({ "type" => "FeatureCollection", "features" => [] }, JSON.parse(File.read(path)))
   end
 
+  def test_build_offline_only_re_extracts_hiking_trails_for_a_newly_added_country
+    select_regions("SK")
+    Maptool::PmtilesBuilder.build_offline(data_dir: @data_dir, download_extract: fake_download).join
+    File.write(@log, "")
+
+    select_regions("SK", "AT")
+    Maptool::PmtilesBuilder.build_offline(
+      data_dir: @data_dir,
+      download_extract: fake_download,
+      fetch_last_modified: ->(_url) { "Wed, 10 Sep 2026 08:00:01 GMT" },
+    ).join
+
+    # SK's cached extract is already newer than SK.osm.pbf (untouched
+    # since the first build), so only AT's hiking trails get (re-)extracted
+    # — SK.osm.pbf itself is also skipped by cached_extract's own
+    # Last-Modified check, "osmium merge" runs regardless since two
+    # countries are now selected.
+    assert_equal(
+      ["osmium merge", "planetiler --osm-path", "osmium tags-filter", "osmium add-locations-to-ways", "osmium cat"],
+      log_lines,
+    )
+    assert_equal %w[AT SK], Maptool::PmtilesBuilder.hiking_trails_countries(@data_dir)
+  end
+
   # The actual reasoning: hiking trails are a bonus overlay bolted onto the
   # existing offline.pmtiles build, not the core map — an osmium hiccup on
   # this one step shouldn't take down an otherwise-successful build.