To merge features based on specified attributes.

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28
votes
4answers
16k views

What is the best way to join lots of small polygons to form a larger polygon?

I have the following layer using SRID 27700 in postgis: It's every administrative region in the UK, and (as you can see from the colour grouping) each of them has a text field specifying the county ...
15
votes
3answers
10k views

Is there a dissolve function in PostGIS other than st_union?

I'm looking for a function to dissolve shared boundaries between polygon features in a table. ST_UNION() almost does what I'm looking for, but it creates a multipolygon from all polygons in the layer ...
15
votes
1answer
11k views

Merging adjacent polygons in shapefile that has been split at tile boundaries?

I'm currently using building data from the Ordnance Survey Vectormap District and I've noticed that a lot of building polygons are split in 2 because of the way the OS split up the shapefile. This is ...
14
votes
2answers
21k views

Merging polygons in shapefile based on field values?

I have a shapefile with a lot of polygons in it. These polygons are grouped into a category: district. How can I merge the polygons based on the same name of the category within this shapefile?
12
votes
4answers
1k views

Grouping corner-touching contiguous polygons using ArcGIS Desktop?

Using ArcGIS 10, I have a Feature Class which I converted from a Raster (GRID) (Raster To Polygon Tool). There are approx. 180,000 polygons. The attribute table contains a [grid_code] field which ...
10
votes
3answers
5k views

Table equivalent to Dissolve for features in ArcGIS for Desktop?

I have a data table that I need to trim down, merging records which have the same value in an ID field and performing a couple math operations on various other fields (summing, averaging). The ...
10
votes
2answers
4k views

How do dissolve polygons from shapefile using open source tools?

In my current project I'm visualizing data on a map representing some values for each administrative areas of a country. I'm given a shapefile of this country, which I'm converting to GeoJSON for use ...
9
votes
3answers
29k views

How to dissolve overlapping polygons?

I have a query regarding the dissolving of polygon features in ArcGIS 9.3. I only have the bare-bones license and an extremely basic knowledge of VB. I have a large shapefile with around 4500 ...
9
votes
4answers
9k views

Dissolve not working in ArcGIS 10

The dissolve tool is not working for me when I use ArcGIS 10. It works perfectly when I use version 9.3. Any help?
9
votes
6answers
9k views

How to fix quickly a lot of geometry validity errors in QGIS?

I am working on ownership data at a US county level. I have one shapefile per county that contains thousands of tax parcels. I need to dissolve the polygons representing parcels owned by the same ...
9
votes
4answers
22k views

How to Merge/Dissolve Polygons By Common Attribute Field in QGIS?

I have joined corresponding Local Enterprise Partnerships table data into a polygon shape file containing UK Local Authorities. How do I Dissolve or Merge the the Local Authorities polygons by ...
8
votes
2answers
454 views

Does dissolving features improve geoprocessing efficiency?

I have a large set of line data (>140,000 features). Is there a processing advantage, in either time required or (more importantly) memory used: to running Dissolve on the data before running Buffer?...
8
votes
3answers
2k views

Dissolve or unsplit lines on common attributes in PostGIS or GRASS?

I have a road centerline shapefile that has roads split at every intersection. However, I would like to join LINESTRINGs that have a common set of attributes into a single LINESTRING. So long as the ...
7
votes
2answers
5k views

Dissolve polygons in QGIS (GEOS) with tolerance

I have a polygon vector layer representing the area inundated in a flood. The layer has been produced in a such a way that some of the areas are composed of multiple smaller touching polygons (see ...
7
votes
1answer
1k views

Dissolving shapefile but retain attribute fields

Is there any way to dissolve shapefile but keep attributes fields in the same time? This is how I want to retain fields: There are two fields I want to conserve in a shapefile. The first column is ...
7
votes
4answers
5k views

Dissolve ploygons in QGIS or Grass to new polygons of defined population sizes

I have a shapefile with 3800 polygons representing the smallest administrative areas in Ireland. Many of these, in rural areas, have tiny populations, under 100 people. In urban areas, all would have ...
6
votes
4answers
2k views

Improving upon ArcGIS Buffer/Dissolve performance?

I'm wondering if anyone else has experienced significant performance penalties when using the ArcGIS buffer function with the 'dissolve' option on point features. My dataset is a shapefile of 260 ...
6
votes
4answers
1k views

How to Unsplit/Dissolve multiple touching lines in Stream Network?

I am trying to dissolve multiple lines for stream networks into individual features. The dataset contains many stream networks so a complete dissolve of the whole dataset wont do as I would like to ...
6
votes
5answers
1k views

Dissolving polygons fails on computers with small amount of RAM

When I'm trying to dissolve a polygon through an arcpy script the operation fails with the 999999 error on computers with small amount of RAM [~3 GB] (known issue). Unfortunately neither this, that ...
6
votes
1answer
1k views

How to achieve equivalent to Dissolve from ArcGIS for Desktop using ST_Union?

I am trying to achieve an equivalent to the Dissolve tool from ArcGIS for Desktop using ST_Union from PostGIS but it seems I am not getting expected result. I have one table which has certain ...
6
votes
2answers
26k views

How to combine adjacent polygons sharing similar trait into single polygon?

I have a large dataset of habitat classes which I have further simplified down into my own unique classes. However, it resulted in there being habitats adjacent to each other with the same forest ...
6
votes
1answer
236 views

Deleting 'garbage' nodes after polygon dissolve

I work with QGIS 2.10.1 on Windows 7 (x64). I have dissolved polygons from an attribute value and the polygons geometries being not perfectly joined together, I get some 'garbage' nodes I need to ...
6
votes
2answers
211 views

Select 90% matching attributes

I have a shapefile (.shp) of 180k roads with information of street name. I need to do a Dissolve on that road network to make only one feature per name. But I have a problem by doing that task ...
6
votes
1answer
163 views

Create buffer based on polyline without line end caps and without dissolving the created polygons in QGis

I have a projected line layer (Shapefile) in QGIS. For every line segment I want to create a polygon without line end caps. The resulting polygone should not be dissolved to a single one. I tried ...
6
votes
0answers
1k views

How to create point labels from midpoints of road polylines in QGIS?

Heres what i want to achieve: i have a roading polyline layer (singlepart ie has several features per road, grouped by an id field), and i want to (after merging the parts) find the mid point of the ...
5
votes
6answers
819 views

How to divide a feature class into ranges?

I have a shapefile consisting of around 4000 polygons. The polygons are created from buffering around a similar number of islands somewhere in the Norwegian archipelago. Due to an error in the ...
5
votes
3answers
2k views

What dissolve tool in QGIS allows me to summarize statistics for multiple attributes?

Is there a tool or plugin in QGIS that resembles ArcGIS 10's Dissolve tool? I'm trying to dissolve several polygons (parks) around the boundaries of another layer of polygons (cities), while ...
5
votes
1answer
2k views

Dissolving specific polygons inside SearchCursor with Python in Arcmap

I have a layer with catchment polygons. For those that are smaller than a certain size, I want to merge with an adjoining polygon (namely the one downstream). In the attribute table I have a GridID, ...
5
votes
1answer
117 views

Dissolve overlapping polygons according to percent overlap using PostGIS?

I have a shapefile with convex hull polygons, all in the same layer/shapefile. Some of the polygons overlap (not duplicate polygons). I would like to dissolve/union the polygons which overlap with ...
5
votes
3answers
3k views

Dissolving polygons by attribute within certain distance using ArcGIS Desktop?

In a FeatureClass I have a lot of polygons which contain attributes of different landuse-types. Now I am trying to dissolve those polygons of the same landuse-type, but only if the distance between ...
5
votes
2answers
263 views

Using newly created features in the next part of a python script

Good Afternoon I am trying to write a python script which buffers a large number of features from a geodatabase (but not all) and then dissolves the newly created buffer shapefiles together. ...
5
votes
3answers
128 views

Dissolve overlapping polygons in SAGA

I've got the following (2D!) situation of overlapping polygons: I would like to have the polygon border dissolved such that I have only one polygon left. I thought this was a definitive case for ...
5
votes
1answer
971 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 ...
5
votes
1answer
2k 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 ...
5
votes
1answer
177 views

Automatically build branches of a river network?

A small non-profit specializing in fish habitat restoration, has asked me to link a spreadsheet of field notes to their GIS. What we have is: A spreadsheet of field notes for small fish streams. A ...
5
votes
2answers
1k views

Practical way of managing polygons and unions of them

I have a table in PostGIS with a quite fine partition of a region, which I'd like to dissolve at two higher levels by means of two foreign keys (e.g. municipality and state). The partition is a real ...
5
votes
2answers
107 views

Identifying a cluster of polygons based on attributes

I'm trying to identify a cluster of contiguous parcels that, when combined, add up to at least a given size and, when combined, have an assessed property value less than a given $ amount. I have a ...
4
votes
3answers
3k views

Why is the Dissolve Tool not working?

I'm still having trouble with the dissolve tool and I've tried all of the solutions offered here including moving the process from the background and repairing the geography. I've also tried amending ...
4
votes
4answers
136 views

QGIS classifying vector data

I am trying to classify a shapefile based on rule set, following this tutorial. This is the result: What I want to ask is: 1. How to insert the classification result (water, land etc) into the ...
4
votes
1answer
939 views

“Singleparts to multipart” vs. “Dissolve”

It seems to me that the vector tools "Singleparts to multipart" and "Dissolve" do the same things. Can someone confirm this, please? Or do I overlook something?
4
votes
2answers
967 views

In PostGIS, how do I merge a multilinestring into a single linestring, keeping the pieces in proper order?

I have a multilinestring made up of several pieces, some of which are facing the wrong direction. (Accessible here: http://pastebin.com/89Zcixv5 ) I think what I'm looking for is some utilization of ...
4
votes
1answer
216 views

Issue with dissolving a polygons layer in QGIS 2.4

I downloaded a dataset of roads and parks from OSM. I then buffered the roads and merged with the parks. Now - all i want is to dissolve / union all the features in the merged layer. I fail to do it ...
3
votes
2answers
2k views

Batch Dissolve Polygons based on Attributes in QGIS or FWTools

I was wondering if anyone can help with batching a dissolve. I have a few hundred polygon shapefiles that I want to dissolve based on an attribute. I would like to do this in QGIS or FWTools. Any ...
3
votes
2answers
123 views

Dissolving with PostGIS slow and results in large table?

I am having a table of polygons with some 15 Mio. records. The polygons hold an attribute called "dn" with integer values between 0 and 6. My goal is to simplify that table so that polygons below a ...
3
votes
2answers
3k views

Problem with merging and dissolving a shapefile in R

I am migrating from ArcMAP to opensource GIS. I've succesfully installed R and many packages in a Ubuntu 12.04 machine. I am used to linux and programming in C, but not to R and its syntax. I am ...
3
votes
3answers
3k views

Want to dissolve adjacent polygons but no common edges

I have a bunch of parcel data, I want to join the polygons basing on the same owner name. Even they are not touched, I want merge them together, such a 100 feet tolerance. The purpose is to show the ...
3
votes
1answer
2k views

Using ModelBuilder to select layers by attributes, dissolve and then merge them?

I would like to reclassify polygons, I want to combine smaller polygons into bigger polygons based on their ID (each polygon has a unique ID). I want to regroup ~800 polygons into ~60 polygons. So in ...
3
votes
1answer
118 views

Converting Road Lines to a Binary Raster Image

I got road data from the USGS database and imported it into QGIS. And I want to transform it into a binary raster image that looks like this in QGIS (this is only a processed screen shot but I want ...
3
votes
1answer
233 views

QGIS 2.4.0: dissolve tool renders artifacts / errors

The dissolve tool (vector>geoprocessing tools>dissolve) renders some artifacts on shapes with high number of polygons. I’m using a shapefile with 3222 polygons and I’m trying to dissolve it using the ...
3
votes
1answer
198 views

v.dissolve to multipolygon

Using v.dissolve in GRASS, I'd like to get a multipolyon as a result. However, I end up with distinct polygons with the same 'dissolve value.' For example; lets assume I have two polygon features ...