How to load world coasts data into PostGIS and query into

gistfile1.txt

Download "Format: Shapefile, Projection: WGS84 (Large polygons are split, use for larger scales)" from:
http://openstreetmapdata.com/data/land-polygons

Import into PG database with PostGIS extension:
shp2pgsql -s 4326 land_polygons.shp | psql <database>

Add index:
CREATE INDEX idx_land_polygons_geom ON land_polygons USING gist(geom);

Query example:
select (count(*) > 0) as aground from land_polygons WHERE st_contains(geom, ST_GeomFromText('POINT(3.007813 46.759292)', 4326));