From c6f1a4112fd1d33e448a9d21c9867ba80a73a2bc Mon Sep 17 00:00:00 2001
From: simonyang08 <ppt5928@gmail.com>
Date: Thu, 17 Sep 2026 18:55:22 +0800
Subject: [PATCH] fix: cap USGS maxZoom at 16 to match tile server capability

The USGS national map tile endpoints (USGSTopo, USGSImageryOnly,
USGSImageryTopo) return 404 above zoom level 16. Verified on
2026-09-17: zooms 8-16 return HTTP 200 while 17 and above return
HTTP 404 for all three services, so the previous maxZoom of 20
produced missing-map areas for users who zoom past 16.

Fixes #570
---
 leaflet-providers.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/leaflet-providers.js b/leaflet-providers.js
index 77e1f39..6574503 100644
--- a/leaflet-providers.js
+++ b/leaflet-providers.js
@@ -1001,7 +1001,7 @@
 		USGS: {
 			url: 'https://basemap.nationalmap.gov/arcgis/rest/services/USGSTopo/MapServer/tile/{z}/{y}/{x}',
 			options: {
-				maxZoom: 20,
+				maxZoom: 16,
 				attribution: 'Tiles courtesy of the <a href="https://usgs.gov/">U.S. Geological Survey</a>'
 			},
 			variants: {