[postgis-users] electronic GIS data scale
pcreso at pcreso.com
pcreso at pcreso.com
Tue Jan 6 11:04:51 PST 2009
I disagree that it is not pertinent to use scale with vector data. I think it can be quite relevant:
Much vector data has been digitised from hard copy. Hard copy always has a scale, which it is useful to record with the digitised data.
Also, Postgis is frequently used as a data server for web mapping applications. These use zoom/scale layers, and different datasets are enabled at different scales. Managing this information in the database is very helpful for data driven applications, which can use this information to generate different outputs depending on the view scale.
I agree that scale is probably not the best way to record data accuracy, or even precision, but it is still a useful & relevant value to record.
--- On Wed, 1/7/09, MarkW <mark.wimer at gmail.com> wrote:
> From: MarkW <mark.wimer at gmail.com>
> Subject: Re: [postgis-users] electronic GIS data scale
> To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Date: Wednesday, January 7, 2009, 3:26 AM
> It might be helpful to think about intended uses of your
> data. You mention
> different digitization methods - if you're concerned
> that these will impact
> data use, then the methods could go in the metadata or
> somehow be encoded
> with the data. If you digitized pond boundaries from aerial
> photos versus
> satellite images, these are different scales - I don't
> know how you come up
> with a precision for that (but the resolution would factor
> in), but I would
> think knowing the digitization method would be helpful -
> i.e. in deciding
> not to do areal calculations below a certain size, etc etc.
> On Tue, Jan 6, 2009 at 8:57 AM, Kristian Thy
> <thy at 42.dk> wrote:
> > On Tue, Jan 06, erik wrote:
> > > This leads to my second question: is it pertinent
> to talk about scale
> > with
> > > electronic GIS vector data
> > No.
> > > and is *scale* the best way to express the
> > > precision of the data given the different
> digitization methods used?
> > Probably not.
> > > Is there another way to express precision?
> > I would use "accuracy in metres" (as in, the
> precision is +/- 5 metres).
> > \\kristian
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