[Qgis-developer] Legend for proportionnal symbols and expression based symbols

[Mathieu Pellerin]

Now that's just gorgeous.




On Wed, Dec 4, 2013 at 7:13 PM, Nyall Dawson <nyall.dawson at gmail.com> wrote:

> I haven't had a chance to properly plan this out, but something which
> has been playing in the back of my mind is the idea of "table
> legends". Take a look at the legend in this map:
> http://www.cartogrammar.com/images/vba/cervical_cancer.jpg
> I'm thinking the user could specify the variable which is changed
> along each axis, along with the min/max value for that axis and number
> of rows/columns for the table. Then the classes would be generated
> automatically (maybe equal ranges? equal count? user specified?) and
> the symbol automatically generated for each cell in the table.
>
> The size and spacing of each cell could be user controlled, so that
> this type of legend would also work for symbol layers.
>
> As I said, I haven't really sat down to work out exactly how this
> would work yet... it's just a rough idea which I've been toying with!
>
> Nyall
>
>
> On 4 December 2013 22:34, Denis Rouzaud <denis.rouzaud at gmail.com> wrote:
> > Hi régis,
> >
> > Martin Dobias will make a proposal soon for a legend refactoring.
> > You should see with him how to let those things happen in the future in
> the
> > new legend.
> >
> > Cheers,
> >
> > Denis
> >
> >
> >
> > On 04. 12. 13 12:08, Régis Haubourg wrote:
> >>
> >> Hi All,
> >> we have a long lasting problem with proportionnal legends in QGIS. It
> gets
> >> more problematic with V2, as those maps are so beautiful and popular.
> >>
> >> I'm starting some brainstorming to clarify fonctionnal specifications
> what
> >> we actually want to have legends in layers registry and composer
> working.
> >>
> >> Here are some exemples of what I would love to see in legends:
> >>   - [0] proportionnal circles or square with 1 to 5 classes
> >>   - [1] proportionnal symbols AND colors
> >>
> >> Now that we have expressions everywhere, we probably will have to handle
> >> legends differently than in other GIS, where legend is generated once,
> >> when
> >> user tune symbology. Let me explain:
> >>
> >> - user can now define expressions for size, color, rotation, border
> >> width...
> >> for any sub-marker (1 to n) of a symbol.
> >> - Moreover, we can use conditionnal expressions, and scale dependent
> >> conditions ($scale variable).
> >> - QGIS is also a server, we need to be able to generate legends working
> on
> >> really displayed datas.
> >>
> >> Conclusion, It now is impossible to correctly pre-generate the legend by
> >> analysing symbology properties.
> >>
> >> Does this sound possible to developpers to explore some other way? We
> >> could
> >> read real dataset to collect informations to build a legend, and
> >> eventually
> >> do some statistical classification to get discrete classes from
> continuous
> >> data?
> >>
> >> We could do that on live or on-demand update maybe.
> >>
> >> My idea was to collect rendered object in current canvas and current
> >> scale.
> >> BUT.. we can face discrete data - some kind of SELECT DISTINCT can do
> the
> >> trick - , OR continuous data - we need then to do some statistical
> >> classification to reduce the legend to 1 - 10 classes to get it
> readable.
> >> We also need some intelligence in those statistical classifications:
> >>   - round values to keep it readable
> >>   - display separate classes only if size or color distance is long
> enough
> >> so
> >> that human eye sees some difference on screen. ie: do not display for
> >> classes if symbol size varies from 0.5 to 0.7...
> >>   - add some options in GUI to choose number of classes, type of legend
> >> rendering..
> >>   - keep the classification process fast (subset of data with random
> >> sampling?)
> >>   - test all use cases, I'm mostly thinking of points symbols, but lines
> >> and
> >> polygons must not be forgotten.
> >>
> >> I'm sure plenty of scientists have already been theorizing all this. Any
> >> opinions? Could this be an idea for GSoC or other kind of training
> course?
> >>
> >> I'll be pleased to get feedback from the community.
> >>
> >> Cheers
> >> Régis
> >>
> >> [0] http://kelsocartography.com/blog/?p=2224
> >> [1] http://www.geoclip.fr/img/bicol.jpg
> >>
> >>
> >>
> >>
> >>
> >> --
> >> View this message in context:
> >>
> http://osgeo-org.1560.x6.nabble.com/Legend-for-proportionnal-symbols-and-expression-based-symbols-tp5092635.html
> >> Sent from the Quantum GIS - Developer mailing list archive at
> Nabble.com.
> >> _______________________________________________
> >> Qgis-developer mailing list
> >> Qgis-developer at lists.osgeo.org
> >> http://lists.osgeo.org/mailman/listinfo/qgis-developer
> >
> >
> > _______________________________________________
> > Qgis-developer mailing list
> > Qgis-developer at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/qgis-developer
> _______________________________________________
> Qgis-developer mailing list
> Qgis-developer at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20131204/1de841c9/attachment.html>