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I'm using QGIS 2.18.27.

I have the following problem: I am trying to create some buffers in the city center, as you can see. And I need to calculate some statistical parameter on every buffer.

map_buffers

As you can see, the Buffer5 area should be used to calculate some statistical parameter, but after I save these Buffers into shapefile, I found that these buffer.shp do not have the original data.

However, I found some other data by using "Identify features" tool, as the picture shows.

buffer_feature_attributes

My question is: Is there actually a way to keep these original data in buffer.shp, that I can use this data to calculate? Or can the original shapefile be split into these buffers, so that I can keep these data?

Taras
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陈柯昊
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1 Answers1

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The data you point in your second picture are in fact in your shapefile but they are hidden in the geometry column.

You could add some of then automatically by using the "Add geometry attributes" tool from the processing Toolbox (I think it will add the surface and perimeter) If you need other properties in your table you could add a new field and use the field calculator to fill it, have a look at the geometry fonction. (be avare that all calculation will use the unit of the layer CRS, if you need meters made sure to use a projected CRS in meters)

J.R
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  • Do you actually mean "Add/Export geometry column"? – Taras Jul 09 '19 at 15:52
  • @Taras in my version (QGIS 3.4.3) the tool is called "Add geometry attributes" and the description read : "This algorithm computes geometric properties of the features in a vector layer. It generates a new vector layer with the same content as the input one, but with additional attributes in its attributes table, containing geometric measurements. Depending on the geometry type of the vector layer, the attributes added to the table will be different.) – J.R Jul 09 '19 at 17:08
  • Thank you for answering. And actually as @Taras said,in my version(QGIS 2.18.27) there's no tool called "Add geometry attributes". Now I use "clip vectors by polygon" tool to cut the buffer I want. Then a new Problem is: I found that these attributes are all the same no matter how big the buffers are. To solve these problem I use "Identify features" tool to get all the real data like "area" and "perimeter",and it worked! But I don't know how to extract these derived data to the attributes. I've tried "Add/Export geometry column" tool and it didn't work. Do you have any idea? Thanks a lot! – 陈柯昊 Jul 10 '19 at 08:44