To merge features based on specified attributes.

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17
votes
4answers
5k 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 ...
12
votes
3answers
6k 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 ...
11
votes
1answer
6k 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 ...
11
votes
4answers
1k views

ArcGIS - How do I group corner-touching contiguous polygons?

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
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
6k 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?
8
votes
2answers
309 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 ...
7
votes
3answers
17k 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 ...
6
votes
3answers
3k 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 ...
6
votes
2answers
11k 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
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 ...
5
votes
5answers
401 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
4answers
2k views

How to improve 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 ...
5
votes
1answer
1k 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
2answers
199 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
1answer
210 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 ...
5
votes
3answers
1k views

Dissolving polygons by attribute and in a certain distance (ArcGIS)

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
4answers
4k 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 ...
5
votes
2answers
119 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 ...
5
votes
1answer
497 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
2answers
818 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 ...
4
votes
2answers
860 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 ...
4
votes
5answers
364 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 ...
4
votes
2answers
1k 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 ...
4
votes
1answer
124 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: 1) A spreadsheet of field notes for small fish streams. ...
3
votes
2answers
1k 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
4answers
148 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 ...
3
votes
3answers
1k 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
2answers
2k 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 ...
3
votes
1answer
1k views

Use model builder to select layers by attributes, dissolve them and then merge them

StackExchange team, 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 ...
3
votes
1answer
64 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
135 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 ...
3
votes
2answers
159 views

Dissolve column based on attribute in another column

I have 3 columns within a polygon layer I'm working with. Column 1 = Landowner, 3 different values Column 2 = Parcel, N different values Column 3 = Management type, 5 different values I would like ...
3
votes
1answer
293 views

How can i merge lines with same name and intersect each other?

I have shp file with 50k lines (roads). Many roads have same name like 'high road' . some of them are the same road (they intersect each other) and some are located in different places of the city. I ...
3
votes
1answer
106 views

How to select polygon close to each other?

I have grass patches and I put a buffer of 250m around them. I did a "dissolve to get larger polygons that overlap, but the attribute table emitted a lot of information, which are important such as ...
3
votes
2answers
332 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 ...
3
votes
2answers
56 views

problem merging polygons based on a column value - using Spatialite

edit: as I am unfamiliar with any tools I decided to try my luck with PostGis. I imported my data. and executed the query : create merged as select delomrade_code, st_union(geometry) from grunnkrets ...
3
votes
0answers
175 views

How to achieve better Dissolve results?

I applied the Vector>Geoverarbeitungswerkzeuge>Auflösen (Dissolve) on a zoning plan (see picture zoning plan). I used the attribute village name as the dissolving criteria. The resulting geometry for ...
3
votes
0answers
867 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 ...
2
votes
2answers
202 views

Why is my dissolve not outputting my features correctly?

I have a parcel polygon layer consisting of ~30,000 polygons that can have one of three values for city limits: 0, 1, and null. I execute a dissolve on this layer with "Create Multipart Features" ...
2
votes
1answer
453 views

How to measure the area of polygons within a fishnet

I am currently trying to measure the area of polygons within each square of a fishnet. The aim of what I am doing is to work out the proportion of different agri-environment schemes by 1km squares. ...
2
votes
1answer
46 views

How to dissolve geodatabase map across two subdivision levels in Arcgis 10.2

The existing polygon database contains attribute table with the following structure, and has three levels; country, state, and city (and many other countries not listed below). I want to dissolve the ...
2
votes
1answer
332 views

Dissolve features in ArcGIS using multiple attributes

This may sound simple, apologies if I missed some earlier discussion on same subject. I have a big set of road data with road numbers and also zone numbers . The road names can repeat across the ...
2
votes
1answer
28 views

ArcGIS Dissolve leaving feature snippets in dissolved polyons. Repair doesn't fix

I'm trying to dissolve some low-level polygons, but the result I'm getting has lots of little pieces of lines left floating around in the output polygons. I've tried doing "repair geometry" on both ...
2
votes
1answer
151 views

Merge section polygons in PLSS

I am trying to merge quarter quarter sections of polygons from PLSS into a quarter section. However, I also want it assigned to correct Township/Range/Section while merging. I know I can hand merge ...
2
votes
1answer
2k views

ArcGIS10 - How do I dissolve two different buffers together so they are not overlapping?

I am trying to find out how many registered sex offenders live within 2,000 feet of a school/park in a specific county. The park buffer and school buffer are dissolved but not together. I am also ...
2
votes
2answers
586 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 ...
2
votes
2answers
106 views

arcpy.Dissolve fails; need a arcpy dissolve to multipart workaround

I have a arcpy script in which I am using arcpy.Dissolve on a single feature class with multiple features to get a single multi-part feature in the output. The script is successful only part of the ...
2
votes
1answer
198 views

How to define polygons overlapping each other?

I have a shapefile of landuse in different catchments. I want to calculate the percentage of each landuse category in each catchment using Tabulate Intersection. Before using this tool, I had ...
2
votes
1answer
173 views

Dissolving stream orders using Python rather than VB script?

I've been trying to dissolve streams, using orders programatically and I came across this VB script. The reason is that if I use ArcGIS dissolve, it merges the confluence of the same orders. I would ...