feat: add HIFLD transmission lines dataset

.github/workflows/sync-transmission.yml

@@ -0,0 +1,33 @@
+name: Sync Transmission Lines
+
+on:
+  schedule:
+    - cron: '0 6 1 * *' # 1st of each month at 6am UTC (HIFLD updates irregularly)
+  workflow_dispatch: {} # Manual trigger
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+      - run: npm ci
+      - name: Sync transmission lines from HIFLD
+        run: npx tsx scripts/sync-transmission-lines.ts
+      - name: Install tippecanoe
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y -qq libsqlite3-dev zlib1g-dev
+          git clone --depth 1 https://github.com/felt/tippecanoe.git /tmp/tippecanoe
+          cd /tmp/tippecanoe && make -j$(nproc) && sudo make install
+      - name: Rebuild tiles
+        run: bash scripts/build-tiles.sh
+      - name: Commit & push if changed
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add data/transmission-lines.json public/tiles/transmission-lines.pmtiles
+          git diff --staged --quiet || (git commit -m "data: update transmission lines (HIFLD)" && git push)

.gitignore

@@ -12,6 +12,12 @@ public/data/territories/
 # Power plants JSON in public/ is copied from data/ at build time
 public/data/power-plants.json
 
+# Transmission lines JSON in public/ is copied from data/ at build time
+public/data/transmission-lines.json
+
+# Transmission lines GeoJSON can be large (regenerate from sync script)
+data/transmission-lines.geojson
+
 # PMTiles archives (built by scripts/build-tiles.sh via tippecanoe)
 # Track the .pmtiles files but ignore any extracted/legacy tile directories
 public/tiles/*

app/(shell)/about/page.tsx

@@ -6,7 +6,7 @@ import Link from "next/link";
 const dataSources = [
   { name: "EIA-860", description: "Annual Electric Generator Report — 15,082 power plants, generator details, fuel types, and capacity data" },
   { name: "EIA-861", description: "Annual electric power industry report — utility ownership, customers, sales, and revenue data" },
-  { name: "HIFLD", description: "Homeland Infrastructure Foundation-Level Data — electric service territory boundaries" },
+  { name: "HIFLD", description: "Homeland Infrastructure Foundation-Level Data — electric service territory boundaries and 52,000+ transmission line segments" },
   { name: "CEC", description: "California Energy Commission — CCA territory data and California-specific utility information" },
   { name: "FERC", description: "Federal Energy Regulatory Commission — ISO/RTO boundaries and wholesale market data" },
   { name: "State PUC Records", description: "State Public Utility Commission filings — rate structures and regulatory data" },
@@ -15,7 +15,7 @@ const dataSources = [
 const dataHighlights = [
   { label: "Grid Operators", value: "3,132", icon: "⚡" },
   { label: "Power Plants", value: "15,082", icon: "🏭" },
-  { label: "Grid Infrastructure", value: "ISOs, RTOs, BAs", icon: "🔌" },
+  { label: "Transmission Lines", value: "52,000+", icon: "🔌" },
   { label: "Territory Boundaries", value: "3,000+ GeoJSON", icon: "🗺️" },
 ];
 
@@ -65,6 +65,9 @@ export default function AboutPage() {
             <Link href="/grid-operators">
               <Badge size="lg" shape="pill" variant="info">Browse Grid Operators →</Badge>
             </Link>
+            <Link href="/transmission-lines">
+              <Badge size="lg" shape="pill" variant="error">Browse Transmission Lines →</Badge>
+            </Link>
             <Link href="/power-plants">
               <Badge size="lg" shape="pill" variant="warning">Browse Power Plants →</Badge>
             </Link>

app/(shell)/layout.tsx

@@ -6,6 +6,7 @@ export default function ShellLayout({ children }: { children: ReactNode }) {
     { id: "home", label: "Home", href: "/" },
     { id: "explore", label: "Explore", href: "/explore" },
     { id: "grid-operators", label: "Grid Operators", href: "/grid-operators", activePatterns: ["/grid-operators"] },
+    { id: "transmission-lines", label: "Transmission", href: "/transmission-lines" },
     { id: "power-plants", label: "Power Plants", href: "/power-plants" },
     { id: "about", label: "About", href: "/about" },
   ];

app/(shell)/page.tsx

@@ -13,6 +13,8 @@ export default function LandingPage() {
   // Power plant count is hardcoded to avoid importing the 8.7 MB JSON
   // into the pre-rendered page. Updated by sync-power-plants script.
   const powerPlantCount = 15082;
+  // Transmission line count is hardcoded for the same reason. Updated by sync-transmission-lines script.
+  const transmissionLineCount = 52244;
 
   return (
     <div className="h-full overflow-y-auto">
@@ -49,6 +51,7 @@ export default function LandingPage() {
             { label: "ISOs & RTOs", value: `${isoCount + rtoCount}` },
             { label: "Balancing Authorities", value: `${baCount}` },
             { label: "Power Plants", value: powerPlantCount.toLocaleString() },
+            { label: "Transmission Lines", value: transmissionLineCount.toLocaleString() },
             { label: "Programs", value: programCount.toLocaleString() },
           ].map((stat) => (
             <Card key={stat.label} variant="outlined">
@@ -109,6 +112,21 @@ export default function LandingPage() {
             </Card>
           </Link>
 
+          <Link href="/transmission-lines" className="block group">
+            <Card variant="outlined" className="group-hover:border-brand-primary transition-colors h-full">
+              <Card.Content className="py-6">
+                <div className="text-lg font-semibold text-text-heading mb-1">Transmission Lines</div>
+                <p className="text-sm text-text-muted mb-3">
+                  Explore {transmissionLineCount.toLocaleString()} high-voltage transmission lines (69kV–765kV)
+                  across the US from the HIFLD dataset.
+                </p>
+                <span className="text-sm font-medium text-brand-primary">
+                  Browse transmission lines &rarr;
+                </span>
+              </Card.Content>
+            </Card>
+          </Link>
+
           <Link href="/explore?view=programs" className="block group">
             <Card variant="outlined" className="group-hover:border-brand-primary transition-colors h-full">
               <Card.Content className="py-6">