In set theory, the union (denoted by ∪) of a collection of sets is the set of all distinct elements in the collection. It is one of the fundamental operations through which sets can be combined and related to each other.

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Sum attribute in overlapping polygons

I have a month's worth of snowfall contoured polygons in one feature class. Polygons represent one day and has a field called SNOWFALL. How can I display the total snowfall for the month? I have the ...
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414 views

SQL Server UNion of geography feature returns FULLGLOBE result?

I have some trouble with sql server 2012. I store coordinates of french cities in my database as geography object (with ESRI 4326) and i want to make the UNION of some cities. I have in result ...
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How to add the values of a common field to a field during union

If I have say 3 overlay features; A,B,C each has a field called FIELD_ID If I do a union, I will get 3 new fields in the output: FIELD_ID_1, FIELD_ID_2, FIELD_ID_3 But how do I get just one ...
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How to do union that results to a SpatialPolygonDataFrame in R?

I have the following code coastline<-readOGR(dsn=".",layer="shp") wetlands<-readOGR(dsn=".",layer="shp") wetb<-gBuffer(wetlands,width=500,byid=T) ...
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18 views

QGIS Grid Union Issues

I am trying to create a choropleth map of ice concentration over Lake Erie. I have data for all the lakes (I can clip it all at the end), which are in a point shape file. I have laid a grid over the ...
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37 views

creating a new layer based on colour characteristics

I have 14 polygon layers. I have plotted them as transparent layers, so I can get a final layer with 6 different colours, which represent different categories. I want to create a new layer made by the ...
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350 views

Problem with running Union Tool - Error Code 000229

I have been working through an ESRI Tutorial for GIS Analysis. One of the tasks is to Union two feature classes (Flood Areas and Land Use) which are both polygon feature classes. Each time I attempt ...
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PostGIS: Merge any and all adjacent polygons

I would like to do adjacency tests on a parcel (polygons) layer and merge them if they fit certain criteria (could be size). Per the picture below, I would like to merge polygons 1,2,3 and 4, but not ...
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PostGIS “Overlay” Style Union, not “Dissolve” Style

I'm trying to use PostGIS to do a 'union' of polygons. When I Googled "PostGIS Union", I found the ST_Union function, which performs what I would call a 'dissolve,' not a Union. What I actually want ...
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How to union linestring data distributed on multiple layers?

I have four shapefiles. Each contains a linestring as shown in the image. Each shapefile is represented as its own layer in QGIS. I would like to union these linestrings into one polygon which ...
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78 views

List of vector to one raster in PostGIS

Hi PostGIS developers! I need to rasterize a part of OSM map by coordinates. I found rather good algorithm, but can’t finish it. I have problems in STEP 3. I described all algorithm here – may be ...
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215 views

How can you calculate the union/merge two polygons in ogr2ogr?

I want to calculate the union/merge two overlapping polygons using ogr2ogr (as I have 300+ to do). I want the output to be the same as you would get if you used the 'Merge shapefiles to one' command ...
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How to create a JTS geometry with holes and islands?

I have a JTS multipolygon geometry created by an Polygon array: multipolygon = gf.createMultiPolygon(this.polygons.toArray(new Polygon[this.polygons.size()])); Those polygons can describe holes or ...
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54 views

GDAL equivalent to ArcGIS Union?

I have a single shapefile full of overlapping polygons. The ArcGIS Union tool will generate individual, non-overlapping polygons with that geometry. Is there a way to do this with GDAL/OGR or another ...
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213 views

How to perform a weighted overlay analysis with categorical classed data?

I have several land use layers (vector polygons) that all contain a field about land use in different classification systems and would like to combine them to a single classification. I would like to ...
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23 views

Calculate normalized summary

I am trying to dissolve polygons having unique values for var1 and then calculate values for var2 to var4. Following is the attribute table. Var2 to Var3 values are dependent on the area. Dissolving ...
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154 views

Need advice on converting large geodatabase into shapefile or postgis

tl;dr: I have a fgdb w/ 800k tiny polygons representing high risk flood areas. I need to sum the area of these polygons within each administrative boundary (HUCs) and have a ratio per huc of high risk ...