diff --git a/pages/concepts.map.md b/pages/concepts.map.md
index 4397140..91ffb9c 100644
--- a/pages/concepts.map.md
+++ b/pages/concepts.map.md
@@ -105,6 +105,7 @@
 - https://geodienst.github.io/lighthousemap/
 - https://mapfight.xyz
 - https://twitter.com/leviwesterveld/status/1506253203704356867
+- https://www.loc.gov/resource/g4104c.ct003853/?st=image&r=0.069%2C0.39%2C0.348%2C0.188%2C0
 
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