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QGIS extract average attribute value from layer based on vector

in a single vector layer I have a three of polygons with different field values (e.g1,2,3). How Can I color each field value polygon differently?Add attribute from underlying polygon based on maximum shared areaDirections based on polygon centroid and average/median point of adjacent polygon's touching borderHow to split a single polygon with another polygon (from a different layer) with QgisCreating a heatmap from vector grid and point layer with QGISCreate a raster layer that represents the distance from each polygon cell to the closest point in a bufferHow to get the selected value in a value map with Function Editor in QGIS 3.0.2?One to many intersection of polygonsUpdate/change/commit an attribute/a field value “on the fly” in QGIS 3Update polygon layer with summarized areas from other polygon layer

1

Say I have one layer below with the blue, red, and yellow polygons in the image below. Each of these values has a different value for attribute A. I have a second layer, which denoted by the bold box in the figure below. I would like to find the average value of attribute A within the area spanned by the bold layer. In the example case it should return an average value of 2 since. How would I do this type of calculation in QGIS 3?

qgis qgis-3

share|improve this question

asked Feb 5 at 21:32

JimJim

61

add a comment | 

1

Say I have one layer below with the blue, red, and yellow polygons in the image below. Each of these values has a different value for attribute A. I have a second layer, which denoted by the bold box in the figure below. I would like to find the average value of attribute A within the area spanned by the bold layer. In the example case it should return an average value of 2 since. How would I do this type of calculation in QGIS 3?

qgis qgis-3

share|improve this question

asked Feb 5 at 21:32

JimJim

61

add a comment | 

Say I have one layer below with the blue, red, and yellow polygons in the image below. Each of these values has a different value for attribute A. I have a second layer, which denoted by the bold box in the figure below. I would like to find the average value of attribute A within the area spanned by the bold layer. In the example case it should return an average value of 2 since. How would I do this type of calculation in QGIS 3?

qgis qgis-3

share|improve this question

asked Feb 5 at 21:32

JimJim

61

share|improve this question

asked Feb 5 at 21:32

JimJim

61

share|improve this question

asked Feb 5 at 21:32

JimJim

61

asked Feb 5 at 21:32

JimJim

61

asked Feb 5 at 21:32

JimJim

61

1 Answer
1

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0

You are looking for the Weighted Arithmetic Mean calculation.

There are many ways to do it and all depend on the form and conditions of the input data.

But in short, all seek to perform the following calculation: Add the product of each value by the area occupied, and divide by the total area.

For the proposal of just three polygons, we can see the manual way of doing it.

My layer "polygons_a" has three fields: "id_a", "area_a" and "value_a".

My layer "polygon_b" has two fields: "id_b" and "area_b".

Make the intersection between "polygon_b" and "polygons_a" layers, keeping the "id_b" fields for the input layer, and the "id_a" and "value_a" fields for the overlay layer.

The output is a new "Intersection" layer. Populate a new field with the area of each intersection feature. I am working with a projected CRS and calculating the planimetric areas with the expression: area($geometry). I named that field: "area_int".

Now, you can calculate the weighted average value for the "polygon_b", in that layer, populating a new field with the folowing expression:

(

  attribute( get_feature( 'Intersection', 'id_a', 1), 'value_a') 

  *

  attribute(  get_feature( 'Intersection', 'id_a', 1), 'area_int') 

  +  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'area_int') 

  + 

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'area_int')

) / "area_b"  

The expression is just taking the values and areas of the "Intersection" layer, multiplying them and adding the products, to divide the result by the area of the "polygon_b" feature.

share

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

add a comment | 

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0

You are looking for the Weighted Arithmetic Mean calculation.

There are many ways to do it and all depend on the form and conditions of the input data.

But in short, all seek to perform the following calculation: Add the product of each value by the area occupied, and divide by the total area.

For the proposal of just three polygons, we can see the manual way of doing it.

My layer "polygons_a" has three fields: "id_a", "area_a" and "value_a".

My layer "polygon_b" has two fields: "id_b" and "area_b".

Make the intersection between "polygon_b" and "polygons_a" layers, keeping the "id_b" fields for the input layer, and the "id_a" and "value_a" fields for the overlay layer.

The output is a new "Intersection" layer. Populate a new field with the area of each intersection feature. I am working with a projected CRS and calculating the planimetric areas with the expression: area($geometry). I named that field: "area_int".

Now, you can calculate the weighted average value for the "polygon_b", in that layer, populating a new field with the folowing expression:

(

  attribute( get_feature( 'Intersection', 'id_a', 1), 'value_a') 

  *

  attribute(  get_feature( 'Intersection', 'id_a', 1), 'area_int') 

  +  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'area_int') 

  + 

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'area_int')

) / "area_b"  

The expression is just taking the values and areas of the "Intersection" layer, multiplying them and adding the products, to divide the result by the area of the "polygon_b" feature.

share

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

add a comment | 

0

You are looking for the Weighted Arithmetic Mean calculation.

There are many ways to do it and all depend on the form and conditions of the input data.

But in short, all seek to perform the following calculation: Add the product of each value by the area occupied, and divide by the total area.

For the proposal of just three polygons, we can see the manual way of doing it.

My layer "polygons_a" has three fields: "id_a", "area_a" and "value_a".

My layer "polygon_b" has two fields: "id_b" and "area_b".

Make the intersection between "polygon_b" and "polygons_a" layers, keeping the "id_b" fields for the input layer, and the "id_a" and "value_a" fields for the overlay layer.

The output is a new "Intersection" layer. Populate a new field with the area of each intersection feature. I am working with a projected CRS and calculating the planimetric areas with the expression: area($geometry). I named that field: "area_int".

Now, you can calculate the weighted average value for the "polygon_b", in that layer, populating a new field with the folowing expression:

(

  attribute( get_feature( 'Intersection', 'id_a', 1), 'value_a') 

  *

  attribute(  get_feature( 'Intersection', 'id_a', 1), 'area_int') 

  +  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'area_int') 

  + 

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'area_int')

) / "area_b"  

The expression is just taking the values and areas of the "Intersection" layer, multiplying them and adding the products, to divide the result by the area of the "polygon_b" feature.

share

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

add a comment | 

You are looking for the Weighted Arithmetic Mean calculation.

There are many ways to do it and all depend on the form and conditions of the input data.

But in short, all seek to perform the following calculation: Add the product of each value by the area occupied, and divide by the total area.

For the proposal of just three polygons, we can see the manual way of doing it.

My layer "polygons_a" has three fields: "id_a", "area_a" and "value_a".

My layer "polygon_b" has two fields: "id_b" and "area_b".

Make the intersection between "polygon_b" and "polygons_a" layers, keeping the "id_b" fields for the input layer, and the "id_a" and "value_a" fields for the overlay layer.

The output is a new "Intersection" layer. Populate a new field with the area of each intersection feature. I am working with a projected CRS and calculating the planimetric areas with the expression: area($geometry). I named that field: "area_int".

Now, you can calculate the weighted average value for the "polygon_b", in that layer, populating a new field with the folowing expression:

(

  attribute( get_feature( 'Intersection', 'id_a', 1), 'value_a') 

  *

  attribute(  get_feature( 'Intersection', 'id_a', 1), 'area_int') 

  +  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'area_int') 

  + 

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'area_int')

) / "area_b"  

The expression is just taking the values and areas of the "Intersection" layer, multiplying them and adding the products, to divide the result by the area of the "polygon_b" feature.

share

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

(

  attribute( get_feature( 'Intersection', 'id_a', 1), 'value_a') 

  *

  attribute(  get_feature( 'Intersection', 'id_a', 1), 'area_int') 

  +  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 2), 'area_int') 

  + 

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'value_a') 

  *  

  attribute(  get_feature( 'Intersection', 'id_a', 3), 'area_int')

) / "area_b"  

share

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217

answered 7 mins ago

Gabriel De LucaGabriel De Luca

3,003217