[Gvsig_english] SQRT and proportional symbols

[Simon Cropper (Botanicus Australia Pty Ltd)]

Juan Lucus,

Good point.

Cheers Simon

Simon Cropper
Botanicus Australia Pty Ltd
PO Box 160, Sunshine, Victoria 3020.
P: 9311 5822. M: 041 830 3437.
mailto: scropper at botanicusaustralia.com.au 
<mailto:scropper at botanicusaustralia.com.au>
web: www.botanicusaustralia.com.au <http://www.botanicusaustralia.com.au>


On 3/02/2010 8:12 PM, Juan Lucas Dominguez Rubio wrote:
> Hello Simon,
> Thanks for your feed-back.
> Those symbols are intended to be proportional to the population of 
> each city or town. For example we can see at a glance that the 
> population of Rome is about 4 times the population of Turin 
> (north-west). If you add a constant value inside the formula (such as 
> PI) the proportion between the resulting circles remains unchanged so 
> there is not a difference. In any case, you always have to tune the 
> size of the largest circle, so that it's not too big for the map. So 
> you don't need to add constants to the formula, just keep the Sqrt 
> because if provides the right transformation (in terms of proportion).
> Apart from that, this example illustrates the advantage of 2D symbols 
> over traditional charts:
> http://www.prodevelop.es/files/fm/public/downloads/documents/screenshots/gvsig_desktop/circle_sym.pdf
> Regards,
> Juan Lucas Domínguez Rubio
> ---
> Prodevelop SL, Valencia (España)
> Tlf.: 96.351.06.12 -- Fax: 96.351.09.68
> http://www.prodevelop.es <http://www.prodevelop.es/>
> ---
>
> ------------------------------------------------------------------------
> *De:* gvsig_internacional-bounces at listserv.gva.es en nombre de Simon 
> Cropper (Botanicus Australia Pty Ltd)
> *Enviado el:* mar 02/02/2010 23:13
> *Para:* Users and Developers mailing list
> *Asunto:* Re: [Gvsig_english] SQRT and proportional symbols
>
> Juan Lucas,
>
> You map looks really good.
>
> I was thinking however that if your NUMERIC_FIELD represents population
> size
> assuming the circle area in the legend field is calculated using radius
> wouldn't
> NEW_FIELD = SQRT(NUMERIC_FIELD/PI()) give you a better estimate?
>
> Cheers Simon
>
> Simon Cropper
> Botanicus Australia Pty Ltd
> PO Box 160, Sunshine, Victoria 3020.
> P: 9311 5822. M: 041 830 3437.
> mailto: scropper at botanicusaustralia.com.au
> <mailto:scropper at botanicusaustralia.com.au>
> web: www.botanicusaustralia.com.au 
> <http://www.botanicusaustralia.com.au 
> <http://www.botanicusaustralia.com.au/>>
>
>
> On 3/02/2010 4:57 AM, Juan Lucas Dominguez Rubio wrote:
> > Hello.
> > If your vector layer has a numeric field, you can do this:
> > - Add a new field of type DOUBLE
> > - Use the function SQRT in the field calculator so that
> > NEW_FIELD = SQRT(NUMERIC_FIELD)
> > - In the symbology dialog, choose 'proportional symbol' with your
> > favorite settings.
> > This is what you'll get:
> > 
> http://www.prodevelop.es/files/fm/public/downloads/documents/screenshots/gvsig_desktop/ita.html
> > Circle area (not diameter) is proportional to population.
> > Regards,
> > Juan Lucas Domínguez Rubio
> > ---
> > Prodevelop SL, Valencia (España)
> > Tlf.: 96.351.06.12 -- Fax: 96.351.09.68
> > http://www.prodevelop.es <http://www.prodevelop.es/> 
> <http://www.prodevelop.es/>
> > ---
> >
> >
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