You are right, Calle, cannot use Lat/Lon - but pretty much any equal-area projection should work, right?
Or is your concern that UTM is used? Would be strange to transform to UTM rather than some, Cylindrical Equal-Area function, e.g. Gall-Peters. But I will let Bjørn/Jan respond. k On Mon, Apr 25, 2016 at 3:28 PM, Calle Hedberg <calle.hedb...@gmail.com> wrote: > Knut, > > That makes no sense - nobody does area calculations on lat/long (i.e. the > geographical graticule), you must first project the lat/long data into a > suitable projection and then calculate areas. > > For smaller areas (e.g. small and medium-sized countries) you would > typically use UTM (Transverse Mercator), but that is completely > inappropriate for larger areas. Just think about it: on a standard global > Mercator projection, Greenland looks twice as big as India - whereas the > reality is that India has a 50% larger area than Greenland. > > Besides, if you do calculate areas using lat/long and decimal degrees, the > "result" will be squared decimal degrees - which means nothing to anybody. > > Regards > Calle > > > On 25 April 2016 at 15:16, Knut Staring <knu...@gmail.com> wrote: > >> AFAIK all coordinates are lat/lon, so I suppose that also goes for the >> area calculation. >> >> Knut >> >> On Mon, Apr 25, 2016 at 3:05 PM, Calle Hedberg <calle.hedb...@gmail.com> >> wrote: >> >>> Lars, >>> >>> Thanks - it is downloading >>> >>> One initial question re GIS area calculations: what projection is used >>> for the calculation? >>> >>> regards >>> calle >>> >>> On 25 April 2016 at 14:53, Lars Helge Øverland <l...@dhis2.org> wrote: >>> >>>> >>>> >>>> On Mon, Apr 25, 2016 at 2:39 PM, Calle Hedberg <calle.hedb...@gmail.com >>>> > wrote: >>>> >>>>> Hi, >>>>> >>>>> Good stuff - will go through it in more detail, but please note that >>>>> trying to download the 2.23 demo database gives an error (file not found). >>>>> >>>>> regards >>>>> Calle >>>>> >>>> >>>> >>>> Right - fixed now. >>>> >>>> >>>> -- >>>> Lars Helge Øverland >>>> Lead developer, DHIS 2 >>>> University of Oslo >>>> Skype: larshelgeoverland >>>> http://www.dhis2.org <https://www.dhis2.org/> >>>> >>>> >>> >>> >>> -- >>> >>> ******************************************* >>> >>> Calle Hedberg >>> >>> 46D Alma Road, 7700 Rosebank, SOUTH AFRICA >>> >>> Tel/fax (home): +27-21-685-6472 >>> >>> Cell: +27-82-853-5352 >>> >>> Iridium SatPhone: +8816-315-19119 >>> >>> Email: calle.hedb...@gmail.com >>> >>> Skype: calle_hedberg >>> >>> ******************************************* >>> >>> >>> _______________________________________________ >>> Mailing list: https://launchpad.net/~dhis2-devs >>> Post to : dhis2-devs@lists.launchpad.net >>> Unsubscribe : https://launchpad.net/~dhis2-devs >>> More help : https://help.launchpad.net/ListHelp >>> >>> >> >> >> -- >> Knut Staring >> Dept. of Informatics, University of Oslo >> Norway: +4791880522 >> Skype: knutstar >> http://dhis2.org >> > > > > -- > > ******************************************* > > Calle Hedberg > > 46D Alma Road, 7700 Rosebank, SOUTH AFRICA > > Tel/fax (home): +27-21-685-6472 > > Cell: +27-82-853-5352 > > Iridium SatPhone: +8816-315-19119 > > Email: calle.hedb...@gmail.com > > Skype: calle_hedberg > > ******************************************* > > -- Knut Staring Dept. of Informatics, University of Oslo Norway: +4791880522 Skype: knutstar http://dhis2.org
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