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Is it possible in PyQGIS to have in one layer more polygons and some would have one set of attributes and another different?

E.g. Polygon_1(name, size, average_age), Polygon_2(name, size, average_height), Polygon3(same as Polygon1)...

I imagine that I would create two tables and when I create a new polygon I somehow link it together.
Is anything like that possible? Or do I have to have one layer for each set of attributes?

Joseph
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Aerov
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2 Answers2

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You can have multiple layers (or shapefiles) with different attributes. It sounds like from your description that you want to do a JOIN - which is basically connecting a number of layers together by a common attribute.

So you could, for example, have a single layer which is joined to a number of other layers by using the name attribute. Then that layer will contain all attributes corresponding to the name (it is ideal to use a joining attribute that is unique, otherwise you may not get the correct average height for the correct name).

Joining options

Hope this helps!

EDIT:

@MatthiasKuhn posted an answer to a question I asked using PyQGIS to join layers together. Since you included a pyqgis tag, I thought the following post might help in that regard.

QGIS 2.2 - possible to do a JOINS from the Action list?

Community
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Joseph
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    Just to clarify because I think this is what you mean: one shapefile with only the name attribute, and then a few other a-spatial tables that each have the name attribute but different sets of information. Then add the shapefile a few times to create separate layers and join each a-spatial table to a different layer. So: one shapefile, many tables. – mr.adam Jul 30 '15 at 13:17
  • @mr.adam - Thanks for your comment buddy! Just want to ask, why create separate layers for the shapefile and then join each of those layers with each a-spatial table? Wouldn't it be easier to have a single shapefile joined to multiple a-spatial tables? – Joseph Jul 30 '15 at 13:35
  • I guess it just comes down to what the OP wants, I may have misinterpreted the desired outcome. I was just thinking of a way that the same geometry could be used with layers that have different sets of fields. – mr.adam Jul 30 '15 at 14:40
  • @mr.adam - You should post your suggestion as an answer (I will upvote it) as the method you described could probably be used for PyQGIS :) – Joseph Jul 30 '15 at 14:48
  • Thanks, @mr.adam got it right. Could you also give me a hint how to easily create a-spatial table in PyQGis? – Aerov Jul 30 '15 at 17:48
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Here's what I was thinking, and it's based on the way a lot of attribute-heavy government data is official disseminated (like US soil surveys, etc.):

--Create a single shapefile with an attribute Name to hold your geometry.

--Create series of a-spatial tables, each with different fields but all with the Name field (sorry, not familiar with how to do this in pyqgis, but you could just write .dbfs with a Python dbf module)

--Add the shapefile multiple times to the project (so you have multiple layers referencing the same shapefile)

--Join a different a-spatial table to each layer.

Now you have multiple layers, each with a different set of attributes, all using the same geometry. So if you edit the geometry of features in one layer, it will be reflected in all the others.

mr.adam
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