Questions tagged [differences]

A "difference" operation is a geoprocessing operation that completely removes one overlapping polygon and the intersection of that polygon from the other. It uses one polygon to "take a bite" out of another.

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Using QGIS Difference with Point and Polygon

After installing a fresh QGIS 3.10 version on a Windows computer I recently saw an unexpected behavior of the "Difference" feature from QGIS. (on one of my old computer with QGIS 3.4 it is different) ...
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56 views

Calculate difference of two LineString

The tool I'm developing is written in Java with Spring Boot, using PostgreSQL as database (PostGIS extension). I also make use of GeoTools. I want to calculate the geometrical difference between two ...
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Difference tool QGIS shows too many Differences

After running QGIS Difference Tool, I get a lot of differences, but I don't know where they are coming from. The input files are almost similar... Input Image (overlay input almost the same, but from ...
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1answer
91 views

Finding differences between polygons in PostGIS

I have another redistricting question. The datasets and queries available on my GitHub, but I will include the queries here, too. I am working on two complete datasets: 1) A PLAN - composed of ...
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1answer
70 views

How can I process vector difference between 1 group layer and 1 polygon layer?

I have one layer group called 'left_buffer', containing 40 buffered polygon layers (name: 1,2,3,...,39,40). I want to use difference vector tool between 'left_buffer' and 'bldg' layer, but I'm getting ...
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Inaccurate difference operations in GEOS

I've noticed large inaccuracies in the Django GEOS API's difference operation, see the example below. In [3]: geom1 = GEOSGeometry('{ "type": "Polygon", "coordinates": [ [ [ -19.51171875, 37....
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2answers
80 views

PyQgis difference iteration

I use Qgis. I have two layers that are two circles with the same center. One larger and one smaller. I want to do the difference between the two circles BUT only if they have the same "objectid" (the ...
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2answers
249 views

Doing difference between two layers in PyQGIS?

I'm developing a plugin where I would like to get some features from one layer (a), do a difference on them with the entirety of a second layer (b), and put the results into a layer I've created in ...
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1answer
72 views

Quicker function than dissolve and difference

I'm on QGIS (v. 3.6) trying to create a map of Florida's hydrography using the NHD "Water Areas" shapefile. Methodology is to fix any invalid geometries in the NHD data, dissolve the layer, and then ...
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34 views

Algorithm “qgis:difference” returns multiple heterogeneous outputs

I use the qgis:difference algorithm but it returns multi-type outputs. Sometimes it's a QgsVectorLayer but sometimes a str such as : output_.... My question is : when the algorithm returns an empty ...
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1answer
84 views

Extracting difference between two shapefiles (not symmetrical difference) using ArcGIS Desktop?

I have a shapefile with polygons that portray survey areas (Pink areas in picture below). I receive a new updated shapefile with additional survey areas, and thus new polygons (Green areas in ...
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865 views

Vector difference between two polygon layers by attribute

Is there a way to do a 1:1 difference between two polygon layers based on a similar attribute? The layers have the same number of features with a shared attribute. I've tried the native QGIS ...
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Function in R to get difference between two sets of polygons comparable in speed to QGIS

I have two very large polygon shapefiles for which I need to calculate the difference between the two shapefiles. One is a shapefile of forest polygons, the other is a shapefile of road polygons. I ...
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How do I select rows in an attribute table of a vector layer grid which are outside of another vector layer?

So what I am working on is accessibility analysis, I want to know how many percent of the population of a country have access to certain health services within a given driving time. For example is it ...
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334 views

Difference between two polygons in Earth Engine

I have a reservoir and its buffer (see below). I want to do the difference between the 2 so that my buffer is just a contour around the polygon. I tried the 2 following scripts but cannot get the "...
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1answer
56 views

Using “Difference” geoprocessing tool on Big Data taking a very long time

I am using QGIS Bonn 3.2.3. I've recently been using the Difference function to calculate a list of points and it is taking a terribly long time. I was wondering if you could point out any obvious ...
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1answer
799 views

Comparing two shapefiles(layers) and display the differences in features in MapContent object in GeoTools

I am working with GeoTools libraries to implement GIS features. Here, I have two different shapefiles and I want to generate a new separate layer containing the differences between the two shape files....
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reverse clip (erase) for spatial point data frame (R) [duplicate]

I am trying to recreate the suggestion from this link but instead of using it on a sPolygondf, to do the same for a sPointdf. All is well, but I get an unexpected output - when I do the difference ...
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1answer
1k views

shapely.difference() possible bug or wierd behavior

So, by definition, if we have polygons A and B, A.difference(B) should return: 1) the same polygon if A does not intersect with B 2) the difference of A and B if they intersect 3) empty geometry if ...
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1answer
222 views

Style features based on difference between current date and date in attribute table

In QGIS >2.18, is it possible to style features based on the age gap between the current date and date recorded in the attribute table. For instance I have purchased a significant amount of OS data ...
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1answer
103 views

Area difference between polygon layers

I would like to calculate the difference of area between two polygons. I tried using the Difference tool, but all it does is create lines that are different between my two polygons. I also tried the ...
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273 views

Saga difference vector tool

My QGis Difference tool doesn't work really well, it gives me lots of little squigly lines. i read in the link below there is such a thing as a vector diffence tool from SAGA, but i can't find it. ...
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1answer
119 views

Splitting One Polygon By Boundary of Another using QGIS?

I'm using QGIS 3.0 and attempting to calculate the number of people that fall within a buffer. The population count is a field within my block group polygon layer. I've attached a screenshot, the ...
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1answer
228 views

Processing Problems with the Difference (QGIS) and Erase (ArcGIS) Tool with big data

I am struggling with processing a huge data set. I downloaded it from a German geodata site (https://download.geofabrik.de/europe/germany.html). I downloaded the ZIP of Bavaria and clipped the eight ...
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Methods to differentiate between terrain

I am not specialized in GIS. I have some moisture contour maps, I want to compare each pair to trace the changes between either in a numeric way. I tried to get the mathematical difference between ...
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1answer
539 views

Map statistical significance in the difference of two raster maps

I have two raster maps that are the output of the same model (they describe the same variable) but ran with different parameters and I would like to assess if there is a statistically significance ...
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2answers
468 views

Points and polygons difference issue QGIS

I'm trying to remove points that are in polygons with the basic difference tool (Vector-> Difference). What I see after the operation suits me because all points in polygons are deleted, but as I ...
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436 views

Difference or Erase layer/shp from another layer using GDAL / OGR? [closed]

Gdal is known for being the fastest library for geospatial data processing. I'm using it in my python script and I'm having issues with performance on a specific task which is Erasing a layer from ...
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2answers
86 views

Duplicated Features in point layer

I have duplicated features in point layer (Land Marks) but these duplicate has 2 cases : they might be not all have their center above each other (some have it at center , some is a bit far but its ...
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1answer
471 views

Calculating between today's date and date field in attribute table ofArcGIS Desktop?

I am trying to use DateDiff to calculate the difference between today's date and the initiated date of various projects. I created a new field called "Duration of Day" and I tried the calculation: ...
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1answer
362 views

Count points not in polygon in QGIS (difference between points and layers give unexpected result)

I have a layer of 130 points and another layer of driving distances as 6 polygon features When I use the count points in polygons I get a running total of the number of points in each polygon feature (...
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1answer
60 views

Downloading kmz/shapefile of differences between 2 compared image dates from planet.com?

I'm interested in downloading a KMZ or shapefile of the difference feature when you compare days on planet.com. The images are huge composites so I don't think downloading 7,000 items for each date ...
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1answer
99 views

How to use the method makeDifference in the console?

I would like to do a "difference" between 2 features in PyQGIS. I don't understand how to use the method makeDifference() as shown on the documentation here. It says the parameter to pass the ...
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1answer
997 views

Difference between lines and polygons using geopandas

I wanted to geopandas.overlay() on lines and polygons : get the geometries from the lines that are not in the polygons. I tried using geopandas for this : result = gpd.overlay(my_lines, my_polygons, ...
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1answer
1k views

Difference Between Polygon Layers

I'm trying to get the difference between two polygon layers using the QGIS difference function. These are the two files: Dropbox When I view the attribute tables of both I can see there are 3 ...
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1answer
221 views

Subtract MultiPolygon table from LineString table

I've two tables, one with a roadnetwork and another one with some polygon. The roadnetwork table has a geometry column defined as COLUMN geom geometry(LineString,4326); while the polygon table has a ...
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1answer
517 views

Difference Tool (Polygon) Not Working

Okay so I'm using QGIS 2.10 (a couple of versions out of date, but shouldn't matter much, eh?) on Windows 7, and I can't figure out this supposedly a very basic geoprocessing tool DIFFERENCE. I'm ...
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1answer
497 views

Deleting sliver polygons after difference operation in QGIS?

I'm trying to find the differing polygons between two layers in QGIS. After running the difference operation, however, I get results like this: I am only interested in the solid (blue) polygons, ...
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1answer
165 views

Removing duplicates in lines using PostGIS?

I have a new polyline and need to remove duplicating parts from it. New polyline is compared to other polylines stored in PostGIS table. I have a query that removes duplicates from line newTrack ...
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2answers
863 views

QGIS Difference not working?

I'm trying to simply get the Difference between two sets of lines, but the algorithm returns a copy of either one, depending of the combination of INPUT/DIFFERENCE layer I try. Never the difference. ...
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1answer
871 views

Trouble using ST_DIFFERENCE() function in PostGIS

If have this: CREATE TABLE buff as ( SELECT route_sutton.id, ST_BUFFER(route_sutton.geom, 30) as geom FROM route_sutton ) CREATE TABLE couvert_dif5 AS ( SELECT nextval('temp_id') AS id, ...
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1k views

Remove polygons of one layer from another polygon layer in QGIS

I have two polygon layers, A and B, both in the same projection. I am trying to create a new layer, C, which is all polygons in A less the areas where polygons in A and polygons in B intersect. I am ...
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1answer
85 views

How to use ST_Difference in case of an featureless input table?

I use the query posted below to create the difference of two polygon layers. CREATE VIEW public.v_diff AS SELECT row_number() over() AS gid, subquery.geom FROM (SELECT (ST_Dump(COALESCE(...
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2answers
1k views

How to compare polygon boundaries in PostGIS?

I've to compare two polygon layers, 'land_use' and 'land_parcels', in PostGIS. My aim is to create linestrings, where boundaries of 'land_use' polygons do not match boundaries of 'land_parcel' ...
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1answer
75 views

Comparing areas of overlapping shapes in QGIS

Given SHP files for a country's Districts in Year1 and Year2, how to output a table whose rows state the percentage composition of each Year2 District in terms of portions of Year1 Districts
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803 views

Whats wrong with the difference tool QGIS 2.14.1?

I want to get the difference between two poligons. I compare the result from Arcgis erase tool and QGIS difference. ArcGIS give me that I want, but Qgis don't. Why? QGIS not only give wrong ...
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181 views

QGIS difference output has same number of features

Having a problem with the QGIS Difference feature. Two inputs: a point and a polygon file. I am trying to generate a list of the points that are not covered by the polygons. I am using the "use only ...
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3answers
1k views

Creating rings from existing polygons using QGIS?

I have been given a shapefile from a client that features pivots, yet they were recorded as 10 circles overlapping. The software my company uses requires that these polygons be rings that don't ...
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3answers
990 views

How to create lines to visualize differences between polygon features in PostGIS?

I've a PostGIS table polygon_b with some polygon features. There is also a table polygon_a which contains the same polygons as polygon_b but with minor changes. Now I want to create lines to visualize ...
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2answers
483 views

How to use ST_Difference to create linestrings from non-intersecting polygon boundaries?

There are two tables with polygon features in my PostgreSQL database. I want to create linestring features where the boundries of the polygons are not intersecting. CREATE TABLE schema.poly_a ( gid ...