ST_GeogFromText — Return a specified geography value from Well-Known Text representation or extended (WKT).
geography ST_GeogFromText(text EWKT);
Returns a geography object from the well-known text or extended well-known representation. SRID 4326 is assumed if unspecified. This is an alias for ST_GeographyFromText. Points are always expressed in long lat form.
Add a WGS 84 geography point column to a table.
ALTER TABLE sometable ADD COLUMN geog geography(POINT, 4326);
Populate the geography column from longitude and latitude columns.
UPDATE sometable
SET geog = ST_GeogFromText('SRID=4326;POINT(' || lon || ' ' || lat || ')');
Specify a geography point using EPSG:4267, NAD27.
SELECT ST_GeogFromText('SRID=4267;POINT(-77.0092 38.889588)');
SRID=4267;POINT(-77.0092 38.889588)