[postgis-users] Confusion about projections and Spatial Data

[Rick Zoolker]

OK, I feel like I've got a fundamental block about how spatial data is
actually used in the real world and how spatially aware databases
actually make use of that data.  This is probably quite obvious for
everyone so please bear with me.

I've been playing with a bunch of spatial databases (Oracle, Postgis,
DB2) and from what I can tell, all tend to roughly follow the OGC SFA
spec (Oracle using different terminology).  Now it also seems that the
SFA spec deals EXCLUSIVELY with Cartesian coordinates.  Now here's my
first confusion.  If they only deal with Cartesian coordinates, why do
they allow you to specify SRIDs that are lat/long based.  Will any of
the SFA functions work with lat/long (other than ST_Transform(), which
is actually a SQL/MM and not even included in SFA)??
My next area of confusion is that I've looked at a bunch of data from
people such as Navteq, teleatlas, and a bunch of individual companies
databases, and it seems that every single one ships and stores their
data in lat/long.  So what the heck?  If the tools can't deal with
lat/long, why does everyone ship and store their data in lat/long?
Does everyone project this data before actually loading it into the
db?  Help!?

Now, it appears that Oracle in particular can do some functions with
lat/long directly (the distance calculation comes to mind), and I know
Postgis has some specialized distance functions for geodetic
coordinates, but I'm not sure if that extends to the whole function
set (i.e. can I do an Intersection of two polygons specified in
lat/long coordinates??).  Why doesn't the OGC SFA spec and libraries
support all the functions with geodetic coordinates directly rather
than require projected coordinates?

Finally, how do the analysis and visualization tools that people put
on top of these databases deal with these questions? (e.g. MapInfo,
ArcView, etc.)  They seem to want lat/long data as well, but if you
stored project coordinates in the database isn't there a problem??

HELP!

  -Rick