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.

learn more… | top users | synonyms

3
votes
1answer
62 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 ...
1
vote
1answer
13 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 ...
0
votes
1answer
31 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) ...
1
vote
0answers
37 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 ...
0
votes
0answers
23 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 ...
2
votes
1answer
27 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 ...
1
vote
0answers
48 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 ...
3
votes
5answers
303 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 ...
1
vote
0answers
54 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 ...
1
vote
1answer
48 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 ...
0
votes
1answer
18 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 ...
0
votes
2answers
66 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"), ...
2
votes
1answer
305 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 ...
0
votes
2answers
38 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
votes
0answers
57 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 ...
5
votes
2answers
261 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 ...
0
votes
1answer
37 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 ...
0
votes
1answer
39 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
votes
1answer
49 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 ...
3
votes
0answers
254 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
votes
1answer
83 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 ...
1
vote
0answers
213 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 ...
1
vote
1answer
571 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 = ...
1
vote
1answer
363 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
votes
4answers
226 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
votes
0answers
78 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 ...
3
votes
0answers
146 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 ...
0
votes
1answer
350 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 ...
1
vote
1answer
52 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 ...
0
votes
1answer
167 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
215 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 ...
0
votes
1answer
384 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 ...
0
votes
0answers
154 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 ...
1
vote
1answer
173 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) / ...
0
votes
2answers
55 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 ...
0
votes
2answers
294 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 ...
1
vote
1answer
201 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
votes
4answers
875 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 ...
4
votes
1answer
513 views

What is the FME Equivalent to the ArcGIS Union tool?

I'm attempting to union 2 large featureclasses in ArcCatalog, QGIS, and FME. What is the transformer that would be equivalent to the ArcGIS Union tool?
0
votes
2answers
751 views

postGIS union multiple tables, big dataset, faster approach?

my goal is simple. I want to union a given set of shapefiles. In the shapefile are stored polygons. The data bounding box is germany, so the data is relatively big. I tried to use all functions ...
3
votes
3answers
492 views

Determining the area of each polygon within a polygon boundary?

I have a series of maps representing a 1000m diameter around a point. These maps contain 40 different types of polygons that represent a land use (ex. Corn crop, Pasture). I want to select all ...
1
vote
3answers
669 views

Is there a dissolve / ST_Union function that will close gaps between features?

I've been reading a number of related threads about ST_Union, ST_SnapToGrid and ST_Dump but I haven't been able to solve my problem. The problem is I am trying to merge Tiger/line census tracts that ...
0
votes
1answer
163 views

How to get average polygon? [duplicate]

Is there a way to get an average polygon of unioned stack of polygons in ArcGIS 10.0? I would like to get an average polygon that would be centroid (but polygon) of whole stack of polygons.
2
votes
1answer
1k views

PostGIS Select Union of Polygons

I have a Postgres 8.4 PostGIS 2.0 enabled database and I've loaded it up with a bunch of shapefiles. I'm trying to get the database to do on-the-fly unions of geometries. Here is the query I'm ...
6
votes
3answers
1k views

Which is more efficient process in ModelBuilder - Merge/Dissolve or Union/Dissolve?

I'm creating a model which combines four very large files and dissolves them. At the moment, my workflow uses the Merge tool and then the Dissolve tool. However, I was wondering if using the Union ...
3
votes
1answer
1k views

PostGIS Dissolve/Union close polygons

I have approximately 1 million polygons that have been split by lines. However, this has caused one half of a polygon to be separated by approximately 50cm from its other half. After doing a lot of ...
0
votes
1answer
239 views

st_linemerge does not work

I have two LINESTRING's which intersect by checking with st_intersects. Then i try to collect/union both linestrings into one Multistring, then try to merge with st_linemerge, but it fails with: ...
3
votes
2answers
646 views

PostGIS - ST_Collect but only include POLYGONs not POINTs?

In PostGSI, is there anyway to turn a GEOMETRYCOLLECTION into a MULTIPOLYGON by dropping all non-POLYGONs/non-MULTIPOLYGONs? I'm doing a query that cuts a bunch of geometries (using ST_Intersection) ...
1
vote
1answer
158 views

OGR UnionCascaded gives strange lines (flat polygons)

I'm using OGR to perform a union using UnionCascaded. All my polygons have been created by GDAL polygonize which ensures that all polygons follow pixel edges and should therefore align nicely. But I ...
2
votes
1answer
414 views

SQL Server UNion of geography feature returns FULLGLOBE result?

I have some trouble with sql server 2012. I store coordinates of french cities in my database as geography object (with ESRI 4326) and i want to make the UNION of some cities. I have in result ...