docs for h3HexAreaKm2

docs/en/sql-reference/functions/geo/h3.md

@@ -380,6 +380,42 @@ Result:
 └──────┘
 ```
 
+## h3HexAreaKm2 {#h3hexareakm2}
+
+Returns average hexagon area in square kilometers at the given resolution.
+
+**Syntax**
+
+``` sql
+h3HexAreaKm2(resolution)
+```
+
+**Parameter**
+
+-   `resolution` — Index resolution. Range: `[0, 15]`. Type: [UInt8](../../../sql-reference/data-types/int-uint.md).
+
+**Returned value**
+
+-   Area in square kilometers.
+
+Type: [Float64](../../../sql-reference/data-types/float.md).
+
+**Example**
+
+Query:
+
+``` sql
+SELECT h3HexAreaKm2(13) AS area;
+```
+
+Result:
+
+``` text
+┌──────area─┐
+│ 0.0000439 │
+└───────────┘
+```
+
 ## h3IndexesAreNeighbors {#h3indexesareneighbors}
 
 Returns whether or not the provided [H3](#h3index) indexes are neighbors.