In PostGIS, we are importing various US census bureau shapefiles (with SRID = 4269) using shp2pgsql loader. I have medium-sized database with several tables containing fields of type geography (lat/lon points, polygons, multipolygons, etc) that span locations across the US on which we do various distance calculations, “within” polygon, etc type of geographic functions as well as display data using Google Maps Api. We currently have no geometry type fields (only SRID used in database is 4326 via geography type).
Because they cover a fairly large area and to keep things simple and consistent (avoid projection details etc), I would like to store the census shapes (ie boundaries for states, metros, counties,block groups..) in geography data type instead of geometry as well (unless there is a reason NOT to do this or someone can explain why we should store as geometry instead).
My question is, if I use shp2pgsql loader with –G option to create a MULTIPOLYGON geography field for these boundaries (and thus use a 4326 SRID) does the loader “convert” the data from a 4269 projection to 4326? Is a conversion really necessary? Do I need to first load into temp table with geometry type then perform update to transform/cast into geography type and then store that result?
Thank you for any advice or insight related to this.