A "difference" operation is an geoprocessioning 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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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 ...
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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 ...
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118 views

Clip polygon using buffer

I'm very new to QGIS, so apologies if this is a daft question. I've been trying to resolve my problem for a couple of days and I can't get anywhere. I have searched for similar issues here on SE but ...
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Vector differencing fails in QGIS (due to geometric errors)

I was trying to correct the country shapefile of Uzbekistan for Gas flares: Input layer (the UZB_adm1) differenced by this layer. In QGIS the result was that the overlapping regions - where the ...
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QGIS 'Difference' tool return empty layers

I've been using QGIS's difference tool to create some new layers. All was going well until I hit a number of layers which return a blank layer with no features when I use the difference tool. The ...
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Viewing results of ST_Difference

I've got an ST_Difference query runnning error free in PostGIS, and in PGAdmin I can see the output table but it's not viewable in QGIS - The table name appears in DB Manager but says "There is no ...
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Generating DEM from point cloud and DEM differencing?

I have two point clouds obtained via structure from motion (ground photos of sand-dunes + Visual SfM/Agisoft Photoscan). If I wanted to generate a DEM from these point clouds and difference them to ...
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Calculating area using dissolve and merge but getting shapefiles with empty attribute tables in QGIS?

I have a shapefile of a country with the 29 provinces. I also have shapefiles with the areas which are protected from construction (there are 4 categories for protection, within 4 shapefiles. Some of ...
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Help Needed with QGIS Vector->Geoprocessing Tools->Difference [duplicate]

I'm trying to use the Vector Geo processing Difference Tool in QGIS to "take a bite" out of one polygon using another in another layer. The tool menu Difference icon is exactly what I'm trying to do - ...
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How can I eliminate leftover border/boundary in QGIS?

I am trying to generate a shapefile which contains the unincorporated areas of St. Louis County, Missouri. I'm using two shapefiles: St. Louis County from the 2012 census, followed by St. Louis ...
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How to erase polygon from another in QGIS

I want to erase the pink polygon from the blue polygon. I've tried clip, difference, and symmetrical difference. Clip produces an empty polygon. Difference produces just another blue polygon.
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Raster diff: how to check if images have identical values?

Is there a means to check to see if any 2 given raster layers have identical content? We have a problem on our corporate shared storage volume: it's now so big that it takes over 3 days to conduct a ...
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Graphically depict statistical difference between thematic rasters

The graph shows a regression between two raster datasets with classified tree canopy cover: class 1 = 0-10%, class 2 = 10 - 20% ...class 6 = >60% (Figure 1, Figure 2). The spatial resolution for ...
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How to subtract lines with thickness from polygon

I have a polygon and some lines crossing it. I want to subtract the lines with a certain "thickness" from the polygon, so it splits up into various polygons which do not touch each other anymore. You ...
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OpenLayers rules and context, what is the difference?

OpenLayers.Style employs two properties, "rule" and "context" which accordingly contain an array of OpenLayers.Rule and a set of methods. I have noticed that "context" can somehow substitute "rule". ...
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135 views

A python tool like GNU's diff for shapefiles?

I often use the GNU diff tool to compare two files or even two folders for differences. I was wondering if there is a Python based tool out there that does basically the same for shapefiles? In the ...
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Raster vs Grid vs Lattice terminology?

I have a question about GIS terminology - what is the difference between grid and raster and grid and lattice - in theory?? I thought, that raster is regular network and value is in the cell and the ...
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291 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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What is the difference between mosaicking and merging?

What is the difference betweem image Mosaicking and Merging?
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What is primary difference between ArcGIS for Desktop and ArcGIS for Server?

What is the primary difference between ArcGIS for Desktop and ArcGIS for Server?
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Analyzing differences between two shapefiles to put results into new shapefile?

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 ...