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
3answers
136 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
votes
2answers
518 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
votes
1answer
344 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 ...
5
votes
1answer
764 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 ...
4
votes
2answers
418 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 ...
2
votes
2answers
2k 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
votes
3answers
488 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
votes
2answers
460 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
1k 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
votes
1answer
163 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 ...
0
votes
1answer
238 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
2k 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 ...
6
votes
2answers
845 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 ...
4
votes
1answer
863 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 ...
1
vote
0answers
106 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 ...