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.

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Problem in polygon division using the union tool from QGIS

I am trying to overlay two polygon layers using the union tool from QGIS, to then compute the areas from the resulting polygons. However, in the resulting layer some polygons are not divided as ...
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34 views

ArcGIS Union equivalent in PostgeSQL?

I am using pgAdmin (v.1.22) for my postgres(9.5). I am still fairly new to postgres. I am trying to perform a union(intersection) of multiple layers where there is both complete and no overlap between ...
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1answer
81 views

Count overlapping polygons, including duplicates

I am using ArcMap 10.2.2 (Advanced license, no toolbar add ons/no spatial analyst) on a Windows 7 computer (i7 processor, 8GB RAM). I have used ArcMap for other basic analyses and have only very basic ...
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1answer
35 views

Finding and merging lines that touch in PostGIS?

I would like to select and merge segments that touch like in the image below. My table contains single segments with their own id (shown in the figure), I just want to isolate single "group" of ...
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1answer
24 views

Combining field data from multiple shapefiles into one queryable layer using ArcGIS for Desktop? [closed]

How do you combine multiple field collected data set in shapefile form in to a single layer in ArcGIS 10.3 for Desktop?
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1answer
30 views

Cleaning up inexact polygon unions

I have geography data stored in SQL Server and I am trying to merge polygons from two data sets together. The problem is that they do not line up exactly, so unioning them results in narrow gaps ...
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1answer
36 views

Creating fishnet from thematic polygon data?

I need to create a regular grid containing attributes from other thematic data from ecological data. I am in effect creating a homogenous polygon raster and adding information from another dataset ...
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29 views

Which are the steps the union functon goes through? [closed]

While skimming the union function I could see it works with intersecting bounding boxes, layer features and attributes. But how, exactly does this function work; which are the lines that check for ...
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47 views

Union overlapping shapefiles (poylgons) and merge the attributes where overlap occurs in R

I have 30 shapefiles of overlapping polygons and would like to union them into one shapefile. The attribute table of the 30 layers is exactly the same (two columns, Type and Origin). A new polygon ...
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1answer
45 views

How do I perform a Union (as per ArcGIS and QGIS) in MapInfo

I am running MapInfo 15.0 and need to perform a Union of two polygon layers (i.e. combine the two and preserve all boundaries and associated attributes). I know there is some ambiguity over the term ...
3
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0answers
83 views

Merge line segments by length (in QGIS)

I have a layer containing line segments which are connected by their endpoints (e.g. as within a street network). I'd like to merge (union) polylines within this layer into one feature until following ...
2
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1answer
54 views

Dissolving a TIN using python/ogr binding

I have a TIN model where I remove some of the triangles (see fig. 1). Most of the triangles touch on one edge, some on one vertice. I would now like to generate a polygon shapefile containing the ...
3
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1answer
138 views

Union on lines using ArcPy?

Essentially I want to union multiple (20) congruent line shapefiles, where overlapping line segments in the input shapefiles are combined into a single resulting output shapefile. But I can't union ...
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1answer
28 views

How to add the values of a common field to a field during union

If I have say 3 overlay features; A,B,C each has a field called FIELD_ID If I do a union, I will get 3 new fields in the output: FIELD_ID_1, FIELD_ID_2, FIELD_ID_3 But how do I get just one ...
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1answer
60 views

How to do union that results to a SpatialPolygonDataFrame in R?

I have the following code coastline<-readOGR(dsn=".",layer="shp") wetlands<-readOGR(dsn=".",layer="shp") wetb<-gBuffer(wetlands,width=500,byid=T) ...
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44 views

Overlapping polygons with buffers and need to keep associated data [closed]

I have a point file that has been buffered by 400m. I have overlayed it on top of a polygon file and I need to keep all data that overlaps for each point. What is the best way to do this? I have ...
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27 views

Calculate normalized summary

I am trying to dissolve polygons having unique values for var1 and then calculate values for var2 to var4. Following is the attribute table. Var2 to Var3 values are dependent on the area. Dissolving ...
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1answer
32 views

Alphabetical Sort within a Record

I am performing a union on a polygon feature class with multiple overlapping polygons. Each of the records in the resulting feature class can be thought of as "unique area" polygons made up of the ...
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1answer
267 views

How to create a JTS geometry with holes and islands?

I have a JTS multipolygon geometry created by an Polygon array: multipolygon = gf.createMultiPolygon(this.polygons.toArray(new Polygon[this.polygons.size()])); Those polygons can describe holes or ...
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5answers
371 views

Easy way to sum up a lot of values?

I've got a shapefile that was made by the mother of all Unions. Because of that, it's got about 400 columns, and I want to sum about 100 of them (specifically, the "Score" from each). Is there an ...
2
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0answers
95 views

GDAL equivalent to ArcGIS Union?

I have a single shapefile full of overlapping polygons. The ArcGIS Union tool will generate individual, non-overlapping polygons with that geometry. Is there a way to do this with GDAL/OGR or another ...
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1answer
55 views

Using union and area increases?

I have two layers … assume A and B … one is landuse and one is limit of that. The main reason to union these two layers is to calculate street. But my problem is after I union these two the area ...
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1answer
22 views

QGIS Grid Union Issues

I am trying to create a choropleth map of ice concentration over Lake Erie. I have data for all the lakes (I can clip it all at the end), which are in a point shape file. I have laid a grid over the ...
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2answers
134 views

Shapely (geos) crashes during unary_union

When attempting to union multiple polygons with Shapely 1.5.6 in Python 2.7.9, using GEOS 3.4.2, I get the following error in the underlying C++ code: Assertion failed: (!"should never be reached"), ...
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1answer
517 views

postgis: cluster/group points based on distance

We have a set of thousands of points and want to group all of those which are within 100m distance from each other (to get the centroid from each group). A first idea was to build 100m buffers around ...
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2answers
60 views

Sum attribute in overlapping polygons

I have a month's worth of snowfall contoured polygons in one feature class. Polygons represent one day and has a field called SNOWFALL. How can I display the total snowfall for the month? I have the ...
2
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0answers
68 views

How to union linestring data distributed on multiple layers?

I have four shapefiles. Each contains a linestring as shown in the image. Each shapefile is represented as its own layer in QGIS. I would like to union these linestrings into one polygon which ...
6
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2answers
388 views

PostGIS ST_Union Performance

I'm trying to execute a 'dissolve' operation in PostGIS using the ST_Union command. The input layer is admittedly quite large and complex. By 'large' I mean 57,771 features, with number of vertices ...
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1answer
50 views

creating a new layer based on colour characteristics

I have 14 polygon layers. I have plotted them as transparent layers, so I can get a final layer with 6 different colours, which represent different categories. I want to create a new layer made by the ...
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1answer
52 views

arcpy Union w/No_Gaps puts “0” into blank fields

wanted to overlay two file geodatabase-based featureclasses where one has a smaller extent than the other, but preserve all input features in the output. I used arcpy.Union_analysis. In order to ...
2
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1answer
69 views

Is this Intersect or Union algorithm associative?

Similar to Is the Intersection Operation Commutative? . Spoiler for that one: Intersection is commutative and associative. I've created an algorithm (in PostGIS but the theory would work in other ...
5
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0answers
631 views

PostGIS: Merge any and all adjacent polygons

I would like to do adjacency tests on a parcel (polygons) layer and merge them if they fit certain criteria (could be size). Per the picture below, I would like to merge polygons 1,2,3 and 4, but not ...
3
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1answer
87 views

Unexpected vertices from the ouput of ArcGIS union tool

I have found some unexpected behavior of ArcGIS union tool. My assumption was that this tool will never add any new vertex to the output layer, but this was not the case. I have run the ArcGIS union ...
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370 views

How to perform a weighted overlay analysis with categorical classed data?

I have several land use layers (vector polygons) that all contain a field about land use in different classification systems and would like to combine them to a single classification. I would like to ...
2
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1answer
1k views

GEOS_ERROR: TopologyException: Input geom 1 is invalid: Self-intersection at or near point

I'm using GeoDjango (but I guess this is from the geos library). I have a set of polygons that compose a city surface and I want to merge them into a single one. The code looks like this: polygons = ...
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1answer
963 views

Intersect/union two different polygon layers to produce a third polygon type

Can anyone instruct me on the correct way to union/intersect two different layers containing polygons so that a third layer is created containing the attributes of the non-overlapping regions from ...
3
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4answers
428 views

Is there a union function for multiple layers comparable to ArcGIS in open source GIS like QGIS?

I need a union function for a lot of polygon layers (protected areas of all kind, nature, water etc.) comparable to the union function in ArcGIS. I have only the desktop version from ArcGIS and so it ...
2
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0answers
126 views

List of vector to one raster in PostGIS

Hi PostGIS developers! I need to rasterize a part of OSM map by coordinates. I found rather good algorithm, but can’t finish it. I have problems in STEP 3. I described all algorithm here – may be ...
6
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1answer
254 views

PostGIS “Overlay” Style Union, not “Dissolve” Style

I'm trying to use PostGIS to do a 'union' of polygons. When I Googled "PostGIS Union", I found the ST_Union function, which performs what I would call a 'dissolve,' not a Union. What I actually want ...
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1answer
564 views

Problem with running Union Tool - Error Code 000229

I have been working through an ESRI Tutorial for GIS Analysis. One of the tasks is to Union two feature classes (Flood Areas and Land Use) which are both polygon feature classes. Each time I attempt ...
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1answer
61 views

Union with Concatenated Values

I have a polygon feature class in which the polygons frequently overlap each other. I want to find all of the unique combinations of overlapping polygons within that feature class. I believe I want to ...
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1answer
205 views

How to union polygons and add attribute values of combined output features

I have a layer containing 10 polygons all overlapping at various locations. Each polygon has a value of '1' in a column called "value" How do I Union the polygons (rows) together such that the ...
2
votes
0answers
301 views

How can you calculate the union/merge two polygons in ogr2ogr?

I want to calculate the union/merge two overlapping polygons using ogr2ogr (as I have 300+ to do). I want the output to be the same as you would get if you used the 'Merge shapefiles to one' command ...
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1answer
575 views

Using Union on multiple shapefiles to output single result

Using QGIS 2.2 and Python, I would like to use the Union algorithm on multiple shapefiles (contained in a folder TEST) which would then produce single shapefile containing all the data. Currently ...
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0answers
216 views

Need advice on converting large geodatabase into shapefile or postgis

tl;dr: I have a fgdb w/ 800k tiny polygons representing high risk flood areas. I need to sum the area of these polygons within each administrative boundary (HUCs) and have a ratio per huc of high risk ...
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1answer
267 views

ST_Union to merge tables containing lines?

I have to build a street network with Postgis that will be used with pgrouting. I have two tables: 1) the_network (182 lines): is a MULTILINESTRING table. Having columns road_name (varchar) / ...
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2answers
58 views

Erase within a feature class - Planar enforcement

I´m using ArcGIS v10 ArcInfo. I´m working with a feature class that has 5 features which are waterdepths (1 to 5m). These features are overlapping each other. What I need, is that they are not ...
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2answers
426 views

Union in QGIS: missing polygon boundaries

I am trying to UNION two shapefiles in qgis. I use the geoprossesing tool UNION. Both sf are in the same coordinate system (same as in the project). In the resulting sf some polygon borders are ...
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1answer
382 views

how to use union tool for merging more than two layers?

I want to combine different layers into one but I still want to identify different layers in the new combined layer. Union is best for this, but it doesn't allow me to combine more than two layers. I ...
3
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4answers
1k views

How to merge many shape with the same name in different folders?

I've many (hundreds) shape (3D points and 3D polygons) that have the same name, saved in different folders; and I've tried to merge them using batch with Merge tool in ArcGIS... but inexplicably ...