diff --git a/backend/src/Command/GenerateTilesCommand.php b/backend/src/Command/GenerateTilesCommand.php
index a33d024..cd00150 100644
--- a/backend/src/Command/GenerateTilesCommand.php
+++ b/backend/src/Command/GenerateTilesCommand.php
@@ -38,9 +38,9 @@ class GenerateTilesCommand extends Command
 
         // Observations
         $io->section('Observations');
-        $geojson = $this->queryObservationsGeoJSON();
-        if ($geojson !== null) {
-            $this->runTippecanoe($geojson, $tilesDir . '/observations', 'observations', $io);
+        $geojsonFile = $this->queryObservationsGeoJSON();
+        if ($geojsonFile !== null) {
+            $this->runTippecanoe($geojsonFile, $tilesDir . '/observations', 'observations', $io);
         } else {
             $io->warning('Aucune observation récente — tiles non générées.');
         }
@@ -48,9 +48,9 @@ class GenerateTilesCommand extends Command
         // Prévisions par horizon
         foreach (self::TILE_HORIZONS as $horizon) {
             $io->section("Prévisions H+{$horizon}");
-            $geojson = $this->queryForecastsGeoJSON($horizon);
-            if ($geojson !== null) {
-                $this->runTippecanoe($geojson, $tilesDir . '/forecasts/h' . $horizon, 'forecasts', $io);
+            $geojsonFile = $this->queryForecastsGeoJSON($horizon);
+            if ($geojsonFile !== null) {
+                $this->runTippecanoe($geojsonFile, $tilesDir . '/forecasts/h' . $horizon, 'forecasts', $io);
             } else {
                 $io->warning("Aucune prévision H+{$horizon} — tiles non générées.");
             }
@@ -62,81 +62,99 @@ class GenerateTilesCommand extends Command
 
     private function queryObservationsGeoJSON(): ?string
     {
-        $rows = $this->connection->fetchAllAssociative(
-            "SELECT ST_AsGeoJSON(geometry) AS geometry,
+        // ST_SimplifyPreserveTopology réduit le nombre de coordonnées avant export
+        // (tolérance 0.003° ≈ 300m, suffisant pour zoom 5-12).
+        $result = $this->connection->executeQuery(
+            "SELECT ST_AsGeoJSON(ST_SimplifyPreserveTopology(geometry, 0.003)) AS geometry,
                     COALESCE(afai_mean, 0) AS afai,
                     source,
                     confidence,
                     ROUND(COALESCE(coverage_area, 0)::numeric, 1) AS coverage_km2
              FROM sargassum_observation
-             WHERE detected_at >= NOW() - INTERVAL '30 days'
+             WHERE detected_at >= NOW() - INTERVAL '5 days'
                AND coverage_area > 0
              ORDER BY detected_at DESC"
         );
 
-        return $this->buildFeatureCollection($rows, [
-            'afai'        => static fn($r) => (float) $r['afai'],
-            'source'      => static fn($r) => $r['source'],          // 'Sentinel-2' | 'Sentinel-3'
-            'confidence'  => static fn($r) => (float) $r['confidence'],
-            'coverage_km2' => static fn($r) => (float) $r['coverage_km2'],
+        return $this->streamToGeoJSON($result->iterateAssociative(), static fn($r) => [
+            'afai'        => (float) $r['afai'],
+            'source'      => $r['source'],
+            'confidence'  => (float) $r['confidence'],
+            'coverage_km2' => (float) $r['coverage_km2'],
         ]);
     }
 
     private function queryForecastsGeoJSON(int $horizon): ?string
     {
-        $rows = $this->connection->fetchAllAssociative(
-            "SELECT ST_AsGeoJSON(geometry) AS geometry, confidence
+        $result = $this->connection->executeQuery(
+            "SELECT ST_AsGeoJSON(ST_SimplifyPreserveTopology(geometry, 0.003)) AS geometry,
+                    confidence
              FROM sargassum_forecast
              WHERE time_horizon = :horizon
-               AND computed_at >= NOW() - INTERVAL '30 days'
+               AND computed_at >= NOW() - INTERVAL '5 days'
              ORDER BY computed_at DESC",
             ['horizon' => $horizon]
         );
 
-        return $this->buildFeatureCollection($rows, [
-            'confidence' => static fn($r) => (float) $r['confidence'],
+        return $this->streamToGeoJSON($result->iterateAssociative(), static fn($r) => [
+            'confidence' => (float) $r['confidence'],
         ]);
     }
 
     /**
-     * @param array<array<string, mixed>> $rows
-     * @param array<string, callable(array<string, mixed>): mixed> $props
+     * Écrit un FeatureCollection GeoJSON ligne par ligne dans un fichier temporaire.
+     * Évite de charger toutes les géométries en mémoire PHP simultanément.
+     *
+     * @param \Traversable<array<string,mixed>> $rows
+     * @param callable(array<string,mixed>): array<string,mixed> $propsBuilder
      */
-    private function buildFeatureCollection(array $rows, array $props): ?string
+    private function streamToGeoJSON(\Traversable $rows, callable $propsBuilder): ?string
     {
-        if (empty($rows)) {
+        $tmpFile = sys_get_temp_dir() . '/tiles_' . uniqid() . '.geojson';
+        $fh      = fopen($tmpFile, 'w');
+        if ($fh === false) {
             return null;
         }
 
-        $features = [];
+        fwrite($fh, '{"type":"FeatureCollection","features":[');
+        $count = 0;
+
         foreach ($rows as $row) {
-            $properties = [];
-            foreach ($props as $key => $fn) {
-                $properties[$key] = $fn($row);
+            $geom = $row['geometry'];
+            if ($geom === null) {
+                continue;
             }
-            $features[] = [
+            $feature = json_encode([
                 'type'       => 'Feature',
-                'geometry'   => json_decode($row['geometry'], true, 512, JSON_THROW_ON_ERROR),
-                'properties' => $properties,
-            ];
+                'geometry'   => json_decode($geom, true, 512, JSON_THROW_ON_ERROR),
+                'properties' => $propsBuilder($row),
+            ], JSON_THROW_ON_ERROR);
+
+            if ($count > 0) {
+                fwrite($fh, ',');
+            }
+            fwrite($fh, $feature);
+            ++$count;
         }
 
-        return json_encode(
-            ['type' => 'FeatureCollection', 'features' => $features],
-            JSON_THROW_ON_ERROR
-        );
+        fwrite($fh, ']}');
+        fclose($fh);
+
+        if ($count === 0) {
+            @unlink($tmpFile);
+            return null;
+        }
+
+        return $tmpFile;
     }
 
-    private function runTippecanoe(string $geojson, string $outputDir, string $layer, SymfonyStyle $io): void
+    private function runTippecanoe(string $geojsonFile, string $outputDir, string $layer, SymfonyStyle $io): void
     {
         $parentDir = dirname($outputDir);
         if (!is_dir($parentDir)) {
             mkdir($parentDir, 0755, true);
         }
 
-        $tmpFile = sys_get_temp_dir() . '/tiles_' . uniqid() . '.geojson';
-        file_put_contents($tmpFile, $geojson);
-
         try {
             $cmd = sprintf(
                 'tippecanoe -e %s --force --no-tile-compression --layer=%s -Z%d -z%d --drop-densest-as-needed --quiet %s 2>&1',
@@ -144,7 +162,7 @@ class GenerateTilesCommand extends Command
                 escapeshellarg($layer),
                 self::MIN_ZOOM,
                 self::MAX_ZOOM,
-                escapeshellarg($tmpFile)
+                escapeshellarg($geojsonFile)
             );
 
             exec($cmd, $cmdOutput, $exitCode);
@@ -157,7 +175,7 @@ class GenerateTilesCommand extends Command
                 $io->success("→ {$outputDir}");
             }
         } finally {
-            @unlink($tmpFile);
+            @unlink($geojsonFile);
         }
     }
 }