Hot answers tagged spatialite
Lets start with a simple example: spatialite> CREATE TABLE gis193636 (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, flag INTEGER NOT NULL); spatialite> SELECT AddGeometryColumn( 'gis193636', 'geom', 0, 'MULTIPOINT', 'XY', 1); 1 spatialite> INSERT INTO gis193636 (flag, geom) VALUES (1, GeomFromText('MULTIPOINT((0 0))', ...
Your problem is very easy to resolve because the problem is only in the documentation. https://www.gaia-gis.it/gaia-sins/spatialite-sql-latest.html is indeed claiming that ST_Centroid requires Surface but it is not true and you can just feed in your MultiPoints as they are. I made a a following test with spatialite-gui versions 1.8.0 and 2.0.0: Query: ...
In QGIS you'd use the merge shapefiles function, just be sure to choose the correct couples/triplets/whatever. From the program menu, Vector -> Data management tools -> merge shapefiles
Here is a step-wise process. Queries were made with Spatialite-gui and visualizations with OpenJUMP. Take some points into table "points" with an attribute "radius". Buffer points by taking the radius from an attribute with SQL CREATE TABLE "buffers" AS SELECT ST_Buffer("geometry", "radius") as geometry FROM points; Union the buffer areas with SQL ...
You could to use Dissolve Tool But, perhaps you could to create a buffer using the parameter: Dissolve result=YES
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