[Gvsig_english] SQRT and proportional symbols

[Juan Lucas Dominguez Rubio]

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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> Gvsig_internacional mailing list
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