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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GEOS geoprocessing error when using difference tool in QGIS

I am using QGIS version 3.14.0. I have about 20 polygon .shp-files with overlaps between files. All are in the same projection. I've been using the difference tool to remove the overlaps and then ...
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1answer
84 views

Getting the 'composite' of two polygon layers

I have two table of polygons, and I want to 'flatten' them into one table, and have the result tell me which areas are in one table of polygons, which in the other table of polygons, and which are in ...
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1answer
18 views

Difference tool failing for QGIS map layers

I had tried to run the 'Difference algorithm' on two layers. However, the process constantly fails with a "GEOS geoprocessing error: difference failed" message. When I tried running an ...
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51 views

QGIS Difference Algorithm: multilinestring won't work with multipolygon layer

I am working with two vector layers in QGIS (location: Indonesia). I want to 'subtract' the area of layer 1 ('Forest_buffer') of layer 2 (Scenario_1). I am using the Difference algorithm. Layer 2 is ...
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1answer
59 views

Compare two layers and find the percentage of the shared areas that are different between them

I have two shapefiles that identify flood zones for the same general area but in different years. The maps, however, do not cover exactly the same geographical areas (e.g., shapefile 1 covers counties ...
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40 views

PostGIS - ST_Difference creates extra line segment

I have some line of sights from one point, collected into a multilinestring. I want to cut the multilinestring using PostGIS' ST_Difference and a border-dataset (a single multipolygon). I used this ...
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1answer
120 views

Using PostGIS to find the overall difference between two (large) polygon datasets

I need to get the Difference of an input layer with ~30k polygons and an overlay layer with ~500k polygons (of which ~200k intersect the input layer). I am trying to learn PostGIS to do this, as it ...
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0answers
71 views

PostGIS: Using ST_CoveredBy (or similar) to speed up Difference on large datasets?

I need to get the Difference of a single large-area polygon (input layer) and a very numerous set of polygons (overlay layer). The overlay layer has ~500k polygons, of which ~200k intersect the input ...
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16 views

Difference between overlapping polygons using OGR

I’m trying to do a simple difference between two polygons using ogr, but I can’t make it work. The input layers have the same CRS. The input polygon is a multipolygon, and the overlay polygon is the ...
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2answers
43 views

QGIS v/s MapInfo - Differences in Distance Measurements

Distance calculated in different software (MapInfo and QGIS) has given me differences in distance values. To be more precise, it's mostly happening when the distance is more than 25 miles. I doubt ...
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1answer
36 views

Difference tool for rasters

I am using QGIS 3.16.0 and I need to find the difference between two rasters that overlap in some areas (basically I need the areas that are not overlapped). First, I tried polygonizing the smaller ...
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3answers
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Creating 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
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Comparing 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
125 views

Select points outside of polygon in Google Earth Engine

I understand how to get the points that fall inside a polygon with GEE: // Load a feature collection and a area of interest var dataset1 = ee.FeatureCollection("link/to/any/point/dataset/on/gee&...
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1answer
3k views

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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58 views

“difference” between two rasters using raster calculator QGIS

I am struggling to find the right equation to use in the raster calculator to achieve my desired result. Essentially, I have two rasters, with an overlapping portion. See img below: I want to only ...
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1answer
135 views

QGIS difference operation with XYZ tiles

I have a regular layer from a database containing WKT polygons. I'm also using a XYZ Tiles layer of Google Maps. I would like to perform the Vector > Geoprocessing Tools > Difference operation ...
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164 views

Symmetrical Difference using fiona and shapely

I have a polygon that I want to merge into an existing polygon. To do this I first need to run symmetrical difference between the two overlapping polygons, and then merge them. Before symmetrical ...
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1answer
145 views

Difference in geometries of shapefiles

I have the geometry of the outline region as part of one shapefile (which is only one feature and there are other features in it apart from this). Other polygon regions' boundaries which are colored ...
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3answers
25k views

Analyzing differences between two shapefiles to put results into new shapefile using ArcMap

I have two polygon shapefiles of the same region from two different years (1985 and 1997) and I need to analyse the differences between the two shapefiles resulting in a third polygon shapefile ...
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2answers
97 views

Difference between two features in same polygon in QGIS

I have a polygon and some features are below another features. If I would have two different polygons I would use the "Difference" tool so it would take the overlapping feauters to the "...
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1answer
93 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
145 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
119 views

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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1answer
176 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
14k views

Difference between Geographic and Projected coordinate systems?

What is the difference between a geographic coordinate system and a projected coordinate system?
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1answer
77 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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3answers
2k views

Can ogr2ogr “reverse clip” (or “clip out” or “erase” or “difference”) one shapefile from another?

Is there a means in ogr2ogr to "clip out" one shapefile from another? I know ogr2ogr -clipsrc B.shp out.shp A.shp will remove any part of A.shp that is NOT in B.shp. Is there an ogr2ogr command to ...
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0answers
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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
111 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
436 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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2answers
591 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
141 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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0answers
36 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
220 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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1answer
2k 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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0answers
49 views

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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0answers
609 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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1answer
2k 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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1answer
145 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
354 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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0answers
122 views

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
2k 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
304 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
137 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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0answers
344 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
76 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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0answers
30 views

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
629 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 ...