geography:STBuffer() IS 'straight'

It can be difficult to visualize "geographic" straight lines (intersections, overlaps, etc) on a 'flat' projection, so here's a set of STBuffers over the LAX-JFK line... it doesn't "look" straight until you see it on a globe:


Using the 'special columns' feature of Geoquery (and a different map...)

DECLARE @g GEOGRAPHY
SET @g = geography::STGeomFromText('LINESTRING(33 -118, 40 -73)', 4326); 
SELECT @g, 'Blue' AS [COLOR], 2 AS [Thickness]
UNION ALL SELECT @g.STBuffer(450000),  'Blue' as [COLOR], 1 AS [Thickness]
UNION ALL SELECT @g.STBuffer(1500000), 'Green' as [COLOR], 1 AS [Thickness]
UNION ALL SELECT @g.STBuffer(3000000), 'Purple' as [COLOR], 1 AS [Thickness]
UNION ALL SELECT @g.STBuffer(4000000), 'Orange' as [COLOR], 1 AS [Thickness]