At 10:39 PM 03-10-02 +0000, you wrote:

>Thanks for the advice Helen.
>
>I live in Santiago de Chile (that's way south from most of you!)
>which has over 5 mill. inhabitants. The whole city is bounded aprox.
>between [-33.353, -70.790] and [-33.623, -70.492] coordinates.
>
>Having 1 mill. records spread in the above "bi-dimensional address
>space", can be considered "enough granularity"? The probability for
>two rows to be on the exact same latitud or longitud is small,
>perhaps 1 in 500000 (purely subjective number).

It looks just fine.

>Unfortunatly the most frequent constraint (WHERE clause) used for
>geographic display is the map bounding box. When rendering general
>purpose information layers (such as streets, or addresses) the only
>precondition is the desired viewable area.

Then your BETWEEN predicates should be more than adequate, since your
indexes are highly selective. The network traffic might be quite high if
your search was on churches in Santiago. :-))

Helen