Questions tagged [dissolve]

To merge features based on specified attributes.

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47
votes
4answers
34k views

Joining lots of small polygons to form larger polygon using PostGIS?

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 ...
30
votes
5answers
37k views

Fixing 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 ...
23
votes
1answer
19k 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 ...
22
votes
3answers
58k views

Merging/Dissolving polygons by Common Attribute Field in QGIS?

I have joined corresponding Local Enterprise Partnerships table data into a polygon shapefile containing UK Local Authorities. How do I Dissolve or Merge the the Local Authorities polygons by ...
21
votes
3answers
47k 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?
21
votes
3answers
18k 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 ...
14
votes
3answers
8k views

ArcGIS Desktop tool that does for records in a table what “Dissolve” does for features?

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 ...
12
votes
3answers
2k 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 I ...
11
votes
2answers
10k 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 ...
11
votes
3answers
30k views

Merging adjacent polygons using ArcGIS Desktop?

I want to use ArcGIS Desktop to merge adjacent polygons with each other. There is no common field between the polygons and hence the Dissolve tool is not the ideal solution. The polygons that I want ...
11
votes
1answer
4k 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 ...
10
votes
3answers
42k 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 ...
10
votes
2answers
1k views

Creating 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 ...
10
votes
2answers
5k 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
4answers
14k 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
1answer
8k views

Dissolving shapefile but retain attribute fields using ArcGIS Desktop?

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 ...
9
votes
2answers
34k views

Combining adjacent polygons sharing similar trait into single polygon using ArcGIS Desktop?

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 ...
9
votes
3answers
3k 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 ...
8
votes
2answers
572 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
1answer
1k views

Deleting 'garbage' nodes after polygon dissolve [duplicate]

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 ...
8
votes
1answer
2k views

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

I have a road 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 resulting lines. This is for roads ...
7
votes
4answers
3k 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 ...
7
votes
4answers
4k views

Unsplit/Dissolve multiple touching lines in Stream Network using ArcGIS Desktop?

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 ...
7
votes
1answer
1k views

Cleaning large Shapefile using v.clean in order to dissolve features?

I'm having real problems cleaning up and reducing the size of a Shapefile which is published by the UK's Environment Agency. It shows the extents of the LiDAR open data they publish: each polygon is ...
7
votes
3answers
6k 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 ...
7
votes
1answer
3k 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, ...
7
votes
1answer
638 views

Dissolving shapefile but retaining a list of original attribute value in QGIS

How can I dissolve a polygon layer in QGIS based on a single attribute but keep all (or some) other attributes at the same time? This is how I want to retain fields: There are at least two fields I ...
7
votes
1answer
4k 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 ...
7
votes
0answers
214 views

How do I select the longest connected lines from PostGIS ST_ApproximateMedialAxis?

I used PostGIS ST_ApproximateMedialAxis to transform polygons representing mountain ranges into a series of lines. Now, I'd like to select only the "longest" line segment for each group, so that I ...
6
votes
6answers
2k 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 ...
6
votes
6answers
2k 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: arcpy....
6
votes
1answer
2k views

Trouble when Dissolving Geopandas Polygons

I have dissolved polygons with geopandas. However, the head of attribute table became values of this table. How can I fix this trouble? See:
6
votes
1answer
684 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 ...
6
votes
1answer
5k 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?
6
votes
2answers
323 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. ...
6
votes
4answers
7k views

Dissolving 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
1answer
1k 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 ...
6
votes
2answers
378 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
2answers
3k 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 ...
5
votes
2answers
2k views

geopandas dissolve overlapping polygons

Goal is to group polygon (1,2,4) and polygon (3) based on overlap. All polygons are part of the same shapefile layer. In ArcMap I can simply do dissolve and uncheck Create multipart features. ...
5
votes
4answers
5k views

Removing lines from inside polygon in QGIS

Through a "dissolve" process in QGIS, I achieved some defective polygons generated after dissolve process that have some fails, like these in the screenshot: Is there any automatic process I can make ...
5
votes
3answers
754 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 the ...
5
votes
1answer
194 views

Finding centroid of point pairs based on common ID using ArcGIS Desktop?

I want to take a series of point pairs within a single shapefile and find a single centroid point for each pair. For example in the image below, I would like there to be one point "31", one point "32"...
5
votes
3answers
5k 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
1answer
145 views

Using Dissolve and Multipart to Singlepart in QGIS?

I started with a network of polylines. In QGIS I used dissolve to 'merge' all lines according to an attribute value. This did exactly that, but included non-connecting lines which I don't want. I ...
5
votes
2answers
209 views

Usage of QGIS Dissolve geoalgorithm in QGIS Graphical Modeler (2.18.19 LTR)

When I use QGIS Dissolve geoalgorithm as a standalone tool from the Processing Toolbox, the GUI looks like shown below. By selecting the Input layer I am able to chose from its attributes on wich to ...
5
votes
1answer
1k 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
256 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
2k 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
1answer
1k views

Dissolve only overlapping polygons in R

I have a spatialpolygons-dataframe in R that contains overlapping polygon features. I would like to dissolve only the overlapping features into separate polygon features (one feature per par of ...