SQL Server return type: float

CLR return type: SqlDouble

If a geography instance is closed, its length is calculated as the total length around the instance; the length of any polygon is its perimeter, and the length of a point is 0. The length of a GeometryCollection is found by calculating the sum of the lengths of all of the geography instances contained within the collection.

The following example creates a LineString instance and uses STLength() to find the length of the instance.

DECLARE @g geography;
SET @g = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326);
SELECT @g.STLength();

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