Linked Questions

9
votes
1answer
1k views

PostGIS “Overlay” Style Union, not “Dissolve” Style [duplicate]

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 ...
12
votes
6answers
5k views

How do I make a heat or Choropleth map that uses polygons in QGis?

I've been playing around with the heatmap plugin for QGIS and I am wondering if it is possible to make heatmap with using a similar plugin/tool that uses polygons as well as points? I would like to ...
15
votes
2answers
9k views

Polygon overlay with Shapely

I'm trying to capture all the non-overlapping polygons indicated below using Shapely (given polygons A,B & C). Moreover, I'm hoping to do so without iteration, testing for intersect etc. The ...
12
votes
5answers
2k views

Create mosaic like Voronoi Diagram from disjoint polygons

The illustration below shows the problem: as in (a) I have a set of disjoint polygons, as geometries in PostGIS. I need something like (b), the "mosaic" of this set of polygons, building it by a "...
14
votes
3answers
9k views

How could I turn my data into a heatmap / intensity map?

I have database that tracks a large number of entities. Each entity has a 'coverage area' or 'catchment area' - a radius in miles from a specified UK postcode, eg Leyton office 4.3m E11 4LL ...
8
votes
1answer
4k views

Calculating size of particular area below buffer in QGIS?

I have a point shapefile of villages where data was collected in Northern Kenya. I created a buffer around those villages. The second vector layer contains polygons defining areas according to ...
8
votes
2answers
1k views

PostGIS Union Between Two Tables, Preserving Attributes

I'm trying to union US State level upper- and lower-level government boundaries in such a way that generates one PostGIS table with both the upper and lower level names for each shape. In my example ...
9
votes
1answer
2k views

Intersection of multiple layers in PostGIS

I need to write PL/pgSQL stored procedure for calculation of intersection of multiple layers. For example, for three layers A, B, C this function should return ABC geometry: Function takes as input ...
4
votes
2answers
677 views

ST_Intersection of 3 polygons

I am new to postgis and I need to find intersection of three polygons. In my table named "mytable" contains large no of polygon coordinates and grouped into three categories by adding a field called "...
7
votes
1answer
389 views

How to get smallest line segments from intersection + difference of multiple overlapping lines?

Inspired by this question, and this excellent answer. I have multiple overlapping lines and want to extract the complete intersection of them. So from this sample data SELECT id, geom INTO stackex ...
3
votes
2answers
253 views

Is there an equivalent to “keep inner boundaries” in QGIS 3?

At QGIS 3.4.7, I have some polygons that are overlapped and I use Polygon dissolver (by attribute) from SAGA to dissolve then and I check the option "keep inner boundaries", but this tool takes too ...
4
votes
2answers
609 views

Make biodiversity heatmap in QGIS out of polygons and not points

I would like to make a biodiversity heatmap in QGIS out of polygons and not points. I have a shape file made up of many overlapping polygons. I know how to make a heatmap with a set of points by using ...
3
votes
2answers
233 views

Re-order multipart polygons in PostGIS

I have a table with multpart polygon geometry with coordinate system EPSG:4326. I can identify, what are geometries with more than 1 polygons in it. I want to re-order it in a way that the largest ...
4
votes
1answer
191 views

Calculating the number of overlapping polygons in QGIS

I have several polygons drawn in Google Earth, saved as .kml files. They represent the same feature (a lava flow) as identified by different people on satellite images (so one polygon = one person). ...
2
votes
2answers
271 views

What is the proper name for the “Venn diagram” of a set of geometries?

Sometimes, you have a set of overlapping geometries, and you want to generate an output like this: Image taken from this answer. The resulting polygons have no overlaps; each region of space is ...

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