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: 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 ...
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33 views

Query to Dissolve Nearby Polygons on Hive

I am using the ESRI spatial framework for Hadoop, that extends Hive to use spatial types and operations. My objective is to translate a set of simple queries on PostGIS into Hadoop, in order to ...
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1answer
67 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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51 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 ...
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1answer
66 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
40 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 ...
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4answers
127 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 ...
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0answers
50 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 ...
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61 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
114 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
33 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
111 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 ...
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72 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
209 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
103 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
93 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
52 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
188 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
135 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 ...
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4answers
507 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 ...
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1answer
288 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?
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2answers
442 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 ...
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3answers
309 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 ...
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3answers
501 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 ...
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1answer
88 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.
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1answer
882 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 ...
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3answers
772 views

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

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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1answer
976 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 ...
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1answer
211 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: ...
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2answers
484 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) ...
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1answer
138 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 ...
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1answer
339 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 ...
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3answers
124 views

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 ...
7
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2answers
369 views

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 ...
2
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1answer
249 views

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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1answer
552 views

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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2answers
374 views

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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2answers
1k views

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 ...
5
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3answers
387 views

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 ...
6
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2answers
389 views

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 ...
2
votes
1answer
818 views

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 ...
2
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1answer
147 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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1answer
177 views

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 ...
4
votes
2answers
1k views

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 ...
5
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2answers
644 views

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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1answer
733 views

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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102 views

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 ...