[Qgis-user] Re: [Qgis-developer] Re: New Symbology : merge borders on nodes for lines

[Ramon Andinach]

On 17/02/2011, at 22:26 , Ramon Andinach wrote:
> On 17/02/2011, at 20:59 , Martin Dobias wrote:
>> On Thu, Feb 17, 2011 at 1:33 PM, kimaidou <kimaidou at gmail.com> wrote:
>>> 2011/2/17 Carson Farmer <carson.farmer at gmail.com>
>>>> Perhaps 'Symbol layer ordering' or simply 'layer order'?
>>> 
>>> I dislike "layer order" as it is confusing : do we speak of layers from the
>>> canvas ? Or "style" layers ?
>>> For me we should use the term "layer" in Qgis only for vector and raster
>>> layers
>> 
>> Frankly, with the introduction of symbology-ng I have created some
>> mess in the terminology and I am not sure how to get out of this.
>> Where are the problems:
>> - "style" - before the style referred to Layer style (i.e. renderer,
>> labeling). symbology-ng uses this term for a collection of symbols
>> (and other visual items)
>> - "color ramp" - a convenient source of colors for symbology-ng.
>> Shouldn't that be called a "colormap" since it could be either a color
>> gradient, colors from a palette or just a bunch of random colors?
>> - "layer" - there are map layers and there are symbol layers. I think
>> that generally speaking, a layer always means a map layer.
>> - "categorized" / "graduated" renderer - I remember Carson raising the
>> discussion that these terms are not very clear
>> 
>> An insight from a english native speaker and preferably a user of
>> several GIS would be valuable. It would be good to disambiguate the
>> terms.
> 
> If you'll count an Australian as an English speaker...
> 
> I'd prefer "colormap", for the reason that you give.
> 
> With "categorized" and "graduated" I think that they are clear enough, but not what I would expect. If you were making a graph I was taught "discrete" and "continuous" to describe these data types, and that is what I'd expect. 
> The problem is categorized. Categorized data is data that's been grouped into subsets (bins). So even the "graduated" data becomes categorized. 
> (Take a set of numbers between 1 and 50 {1,2,11,13,22,24,33,35,44,46}, which I treat as "graduated" data. I could then categorize them into 5 groups of equal ranges {1,2}{11,13}{22,24}{33,35}{44,46} )
> 
> For the rest, I've not really used the new symbology enough to comment on.
> 
> I've some experience with Mapinfo and I don't think they way it did symbols is comparable to this. This is better.

I've been thinking on the MI way overnight. In Mapinfo, what the symbology does is seperate to the layer properties, and is called creating a thematic map. These thematic maps are quasi-layers that you can turn on and off, but are only visible if the parent layer is visible. You can create themes by a number of different methods, but the ones I remember (it's been a while since I touched MI - been using qgis too much) are "Theme by Range" (= "graduated") which I used a lot and "Theme by Value" (I think!) (="categorized") which I used less. There were others, but I don't remember them at the moment (I see the pictures in the dialogue box, but not the words).

The one good point of this is that you could have one layer and several sublayers looking at different parts of the one file. So in my line of work, I could have a set of point data with assays for different elements, create themes for several of these elements and switch between them quickly and easily. To do this in qgis, I think I would need to open the layer several times and use the symbology for each different element. (please enlighten me if I'm wrong - I'm not going to pretend to be an expert).

The bad bit about this is that there was no way of fixing these themes to a file, only to workspaces (=Project). So currently I have a set of landholding maps that I colour to show their status. In MI I could have created a theme for this data, but I would have had to make it for every workspace I opened the project in. To get around this, I would edit the file, select the shapes of each type and change those to the colour pattern I wanted and save that. I qgis, I open it once apply a symbology to it, "Save as Default" and it's done. Looks the same, whatever project I open it in.

Looking back over this early morning waffle, there are at least two points in here.
1. I like qgis's symbology much more than MI.
2. "Theme", might work as a substitute for symbol "style".

-ramon.