PostGIS geography conversion not working

Question

I am new to PostGIS and QGIS. I am trying to convert geom to geog and then cast it back to geom in order to buffer my streets by 1,000 ft with this query:

SELECT a.gid, (st_buffer(a.geom::geography,304.8)::geometry) as geom, a.street_ext
FROM public.orangeburgroads a
JOIN public.orangeburg b ON st_within(st_centroid(a.geom), b.geom)
LIMIT 1000;

And here is what I am getting:

Does anyone have a clue why I am getting this result?

FYI orangeburg is a municipal boundary and orangeburgroads is a street center-line file.

Answer 1

The coordinates of your data are not geographic, they are Stateplane, SC, Feet, EPSG:3361. I know this because I used your test coordinate and back-projected it to geographics, to see if I landed in Orangeburg:

SELECT ST_AsText(ST_Transform(
  'SRID=3361;POINT(1940865 660341)'::geometry, 4326));

Fix your data, first of all (do this for all the tables where you have projected coordinates, but an SRID of 4326):

ALTER TABLE orangeburgroads 
  ALTER COLUMN geom 
  TYPE Geometry(MultiLineString, 3361)
  USING ST_SetSRID(geom, 3361);

Now, knowing that your coordinates are in feet, just do your buffer query with that knowledge and skipping the trip into geography:

SELECT 
  a.gid, 
  ST_Buffer(a.geom,304.8) AS geom, 
  a.street_ext
FROM public.orangeburgroads a
JOIN public.orangeburg b 
ON ST_Intersects(ST_Centroid(a.geom), b.geom)
LIMIT 1000;