[postgis-users] Basic question #1 Managing temporality in spatial data - MAUP over time

Paul Ramsey pramsey at opengeo.org
Wed Feb 18 16:35:06 PST 2009

Your approach is fine.

If you were dealing with much larger data collection, you'd find that
over time your spatial selectivity starts to go down, as more and more
data piles up in the same x/y area over time. That's when it's time to
add an indexed time-range to your tuples, so that you can
simultaneously index select on spatial and temporal ranges. For that I
would suggest adding a time range column containing 'seg' objects (see
./contrib/seg) with the end values derived from unix timestamps.


On Wed, Feb 18, 2009 at 4:24 PM, Ben Madin <ben at remoteinformation.com.au> wrote:
> G'day all,
> I hope no one minds this, but I have to deal with some changes to my data,
> and thought it might be a good opportunity to ask the basic questions I've
> been dwelling on for some time.
> Having just received a new set of the spatial data I am working with
> (shapefiles of administrative regions), I am unsurprised to find that about
> 15 districts have gone (been amalgamated), some new ones appeared, and
> indeed one entire province removed!
> My intention was to add two columns to my gis data table -
> geom_start_validity & geom_end_validity, and revise my queries (which
> normally are analysing / displaying movement information) to choose the
> appropriate geometry depending on the date range of the query.
> Is the approach sound? (Is this a reasonable idea? Am I completely off track
> here? Will this make my table difficult to index? Should I find all the
> polygons which are the same and delete the duplicates, extending the
> validity dates?)
> (The interface which relates to the entry of movements would also be amended
> to deliver a different set of provinces and districts depending on the date
> of the movements. How I deal with movements that occur over the transition
> is beyond me so far!)
> cheers
> Ben
> --
> Ben Madin
> t : +61 8 9192 5455
> f : +61 8 9192 5535
> m : 0448 887 220
> Broome   WA   6725
> ben at remoteinformation.com.au
>                                                        Out here, it pays to
> know...
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