Questions tagged [union]
In set theory, the union (denoted by ∪) of a collection of sets is the set of all distinct elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other.
294 questions
1 vote
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QGIS Union missing features
I am trying to get the overlap from polygon layers as new polygons. Classifying new polygons based on their overlap with other layers is the goal. I am using union to achieve this. I am getting weird ...
- 11
0 votes
1 answer
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Union process with aggregation/unique feature by overlay with QGIS
I have a very big polygonal layer (over 1 million objects). This layer contains a 'gid' column whose values uniquely identify each object. There is also a 'hierarchy_level_id' column: this string ...
- 1,106
1 vote
1 answer
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Polygon feature with linestring attached or unattached
I used Python GDAL API to union multiple polygons into one single polygon for the CONUS 49 state boundary, and the result shows some artifacts below. What could be the reason for this? I also used the ...
- 330
0 votes
0 answers
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Why "Union" tool doesn't work as "Intersect" tool on the same polygons in QGIS?
I am using QGIS for some basic activities with the land cover vector layer. I clipped the land cover layer using the mask of a polygon (administrative region) from another layer. Then I used the Union ...
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1 vote
2 answers
110 views
Is there a new tool to replace the Saga Polygon Union tool?
In a previous version of QGIS, I used the Saga Polygon Union tool to combine the clipped data from shapefiles containing land use data and shapefiles containing soils data. The overall goal of this ...
- 163
5 votes
3 answers
258 views
Dealing with NULL when using aggregate function in QGIS Expression
How to deal with NULL in QGIS expressions when using aggregate functions such as union? E.g.: geom_to_wkt(union(make_point(1,4), make_point(1,2))) ----> 'MultiPoint ((1 4),(1 2))' geom_to_wkt(...
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0 votes
1 answer
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Using search cursor or select for related table data in ArcPy
I am very new to ArcPy and code. I have about 600 zones that overlay ~8000 different census blocks, which have been divided so that census blocks that aren't fully inside a zone are split, meaning ...
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0 votes
1 answer
101 views
How to associate point to most recent date in overlapping polygons? (Union & v.clean is giving errors.)
I am trying to associate presence points (where a bird was sighted) in a given month (e.g. December 2022) to the most recent fire that occurred in that area. I am planning on generating a raster (5km ...
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1 vote
2 answers
730 views
How to union two polygon shapefiles by one or more attribute fields in QGIS
I would like to union two polygons that have the exact same fields in their attribute tables in QGIS. However when I use the Union tool, it makes an attribute table that has exactly twice the amount ...
- 407
1 vote
1 answer
96 views
QGIS - Unite many lines in a single Multiline (with branches)
I have a shapefile that contains many lines that connect to each other, forming branches, as shown in the picture: How can I join all these lines into a single entity? I want the attribute table to ...
- 368
0 votes
0 answers
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R library or tool to do spatial apportionment
Please tell me there is a package to do spatial apportionment. I find spReapportion on GitHub that's 7 years old and this tutorial, which was made with R 3.0.1 (May 2013). I'm trying to script the ...
- 1,036
2 votes
0 answers
157 views
Using Union tool in QGIS creates gaps and overlaps
After using the Union tool on QGIS I get hundreds of gaps and overlaps between polygons on the resulting shapefile. If I zoom to the fullest on those gaps and overlaps they are always lines, they ...
0 votes
0 answers
218 views
Union tools for polyline in ArcGIS
I'm trying to combine 2 polylines into one with all features and their attributes will be written to the output feature class. I'm trying to use the Union tools but it won't work on polyline, any help?...
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2 votes
1 answer
335 views
Calculate the ratio of intersection to union in using the field calculator in QGIS
I have two separate polygon layers, A and B, of which I want to calculate the intersection to union ratio and store it as an attribute to polygon A. To do this, one needs to divide the area of the ...
- 903
0 votes
1 answer
3k views
Could not add feature with geometry type MultiLineString to layer of type MultiPolygon [duplicate]
I´m trying to make the Union of two shapefiles on QGIS 3.28.9 and keep getting this error message: Feature could not be written to Union_8f811877_53f7_4317_ae22_fe05e7ab9695: Could not add feature ...