[postgis-users] Selecting an SRID

[Edward Q. Bridges]

Hi,

I'm relatively new to PostGIS and to GIS concepts in general, and I'm 
working on a project which has  a goal of being able to identify points 
within regions (basically).

In enabling a geometry column I'm stuck on how to decide on which SRID 
to use.  The data will come into the system as lon/lat; and it will be 
used as both lon/lat (i.e. to show system users points within regions) 
and in meters (i.e. to tell users how far away one point is from 
another).  Other sorts of analyses will be what regions are near a 
region, what points are near a point, and what regions and points are 
enclosed by another region.

Will my choice of SRID affect how efficiently these analyses can be 
done?  Is it possible to use one SRID for all of these different usage 
scenarios?

Thanking in advance for any help, or useful ideas.

Best regards,
Ed