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: [email protected] <mailto:[email protected]> 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:* [email protected] 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: [email protected] > <mailto:[email protected]> > 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/> > > --- > > > > > > _______________________________________________ > > Gvsig_internacional mailing list > > [email protected] > > http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional > > > _______________________________________________ > Gvsig_internacional mailing list > [email protected] > http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional > > > _______________________________________________ > Gvsig_internacional mailing list > [email protected] > http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional > _______________________________________________ Gvsig_internacional mailing list [email protected] http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional
