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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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 ...
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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 ...
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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 ...
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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.
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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 ...
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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 ...
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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 ...
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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: ...
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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) ...
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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 ...
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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 ...
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Iteratively unioning pairs of shapefiles

A simple (I think) Model Builder question. I have 25 field sites, for each of which I have mapped land use as separate layers for different years. In one folder I have veg layers for 1994, named ...
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PostGIS Union Between Two Tables, Preserving Attributes

I'm trying to union US State level upper- and lower-level government boundaries in such a way that generates one PostGIS table with both the upper and lower level names for each shape. In my example ...
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1answer
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Why doesn't PostGIS use gist index when doing a ST_DUMP(ST_UNION)?

My query: DROP TABLE IF EXISTS tmp; CREATE TEMP TABLE tmp AS SELECT *, ST_BUFFER(the_geom::GEOGRAPHY, 3000)::GEOMETRY AS buffer FROM af_modis_master LIMIT 20000; CREATE INDEX idx_tmp_the_geom ON tmp ...
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PostGIS - Why are my ST_Union results (stored in a new table) outputting as points and not polygons?

I've decided to move to PostGIS to merge polygons rather than spend hours doing in in QGIS. However, I'm hitting an issue where the results of an ST_Union query are being stored, or at least outputted ...
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PostGIS algorithm to unite points of two geometries that are within specified radius

I want to find an PostGIS algorithm to unite points of two geometries that are "near" to each other. That is: I want a function, that takes as input two geometries, and returns 1 geometry, that ...
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Merge polygons in postgis

I have a hand-digitized coverage stored in postgis. There, I have a few shiver-polygons I would like to get rid of by including them into one of the neighbouring polygons. are there any commands that ...
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Trying to combine nearby points into a polygon

We have collected millions of cell phone strength readings. I am trying to group points of the same strenght that are within a distance of each other in to a polygon. I asked on the postgis mailing ...
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How to generate discrete areas from multiple, overlapping features?

I have a point dataset that I want to append some information from a polygon to. My polygon shapefile contains over 500 features. Whilst each of these features represents individual areas they are ...
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How to correctly merge layers with overlapping polygons in QGIS/GRASS?

I have 4 vector shapefile that I would like to join/merge, without worrying about attributes. Here are the shapefiles. I would like to do an union and a spatial dissolve, but everytime I do a dissolve ...
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1answer
181 views

Union shapes which is not touching

I want to union two shapes which is not touching each other using Arcobjects. I do not want to perform small buffer on two shapes and union them . This is because when we apply buffer round buffer ...
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overlay a county shapefiles for 2 different years [duplicate]

Possible Duplicate: overlay county shapefiles for 2 different years 2 down vote favorite I have county-level shapefile for South Caroline in 1880 and one for 1940. I would like to overlay ...
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merge shapefile using ogr2ogr and retrieve the attribute of both

Ciao, I have two shape files that I want merge (overlay/intersect) having in the destination the attributes of the two sources file. ogr2ogr file_merged.shp tl_2010_us_uac10_conus_albersUA.shp ...
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memory issue when trying to buffer/union large dataset using postgis

I am trying to generated a dissolved buffer of a large point dataset (Ideally 29 million points - Address data in Great-Britain, but I receive the data by chunks of 1 million points, so these could be ...
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GEOS Python: Taking Union of several geometries

I am using the GEOS/OGR library in Python. I have files full of geometries that overlap, and I want to convert these to files of geometries that don't overlap. The way I have been approaching this ...
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Merge polygons into a single polygon [duplicate]

Possible Duplicate: How to aggregate detached polygons? Is there any open source java library to merge polygons? My use case is that i have a few building feature polygons close by. I need ...
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Eliminating gaps in ArcGIS union operation?

I have a layer that has nested polygons in them. I want to aggregate the polygons. I do this using the Union function. I use the "No Gaps" option when I perform the union. However, when I overlay ...