heat mapqgis
There was already How to build effective heat-maps? from 2010 where the answer was basically "use QGIS Heatmap plugin".
I've also read on QGIS webpage that it is now "implemented as a native C++ plugin"
What is the best way to generate a heatmap from a list of observations, in QGIS?
I've done a bit of work on this in GeoTools/GeoServer by extending the Heatmap Rendering Transformation to support geometries other than points.
It's not finished yet, but you can get the feature branch from my repository on GitHub.
The screenshot is of GPS tracks from when I worked as a pizza delivery driver.
You might want to create centroids for your grid of polygons, then and attach the weight value of the data with no exact location (located in a grid cell) to the centroids. This can be accomplished by:
That should give you the weights (from each polygon in the grid) into a point layer of centroids. Now you can merge these points together with your actual point locations to create one point vector with weights, and do any further heat maps etc.
If you want to total the weight per polygon, that's an additional process. I do these kinds of things in a database. Import both the polygon grid and the points into Spatialite, for example then try these SQL commands in Spatialite-gui:
ALTER TABLE grid ADD COLUMN total_weights REAL;
UPDATE grid SET total_weights=(SELECT SUM(p.weight) FROM points AS p WHERE ST_Contains(grid.geometry, p.geometry));
(Of course, you'll have to adjust the column names and table names)
Best Answer
I've just learned that the heatmap plugin is not part of version 1.7, so if that's what you're using (like I am), it's not here for us to use it yet. If you're using the "trunk" version of QGIS the heatmap can be found under the Raster menu.