[postgis-users] Data storage w.r.t. projections

[Mark Fredrickson]

> One step that's likely useful is to look at the data sources you will
> use and see what they are in.  Most states have a state plane
> coordinate system.  I don't mean you should just use that system, but
> it seems like information you should know when choosing.
>
> Note also that 'UTM zone 15' still needs a datum; NAD27 CONUS and
> WGS84/NAD83 are both commonly used with UTM.

In my particular case, the Minnesota Legislative GIS department
(http://www.commissions.leg.state.mn.us/gis/index.html) publishes most
of its data in UTM 15, NAD83 (Sorry I wasn't more specific in
advance).

I'm still scoping out data sources, but this will at least provide the
basic geo-political boundaries and election data I'm seeking. After
that, I'll probably hit up the Census for anything I can find.

>
>   As I understand it, one of the big advantages of UTM is that is allows
>   for Euclidean geometry, as compared to spatial geometry that would be
>   required for a lat,long format. Does PostGIS use this feature of UTM
>   when computing Distance(), etc?
>
> That's a good question, and also what coordinate system the bounding
> box calculations are in.

I'll probably be doing a lot of geocoding of individuals, and then
matching them against this database of district boundaries. I would
also imagine I'll be doing a lot of "give me the 10 people closest to
me" or "give me everyone within 10 miles" or similar type queries.

It is not expensive to translate individual points into a specific
projection, but I would like to avoid large scale, repetitive
transformations on the overall data set.

So it seems the question of whether PostGIS uses Euclidean geometry
for UTM projections is unanswered?

Thanks for your  thoughts,
-Mark