Sampling raster values at point locations in QGIS – an update

In a by now fairly old post I described how to sample raster values at point location in QGIS. The method I described used the ‘Point Sampling Tool’ addon. However, the function creates a new point layer, which only contains the values extracted from the raster layer. None of the fields in the original point layer is copied to the new one. It is possible to join the attribute table of the new vector point layer with the original attribute table afterwards using a spatial join as explained in that post. However, this will not work if your point data includes points with exactly the same coordinates.

Since I wrote that post, QGIS has come a long way. Continue reading “Sampling raster values at point locations in QGIS – an update”

Sum up values of neighbouring polygons – a GRASS GIS approach

How to sum up values of neighbouring polygons in QGIS? This question was asked on gis.stackexchange, with two interesting answers. One answer explains how to use Spatialite and SQL to achieve this. The other answer, explained in more detail here, presents a script using pyqgis and shapely. In this post I am using an alternative approach, using GRASS GIS. Continue reading “Sum up values of neighbouring polygons – a GRASS GIS approach”

Splitting vector maps in QGIS and GRASS GIS

I am currently involved in a project that is developing a vegetation map for eastern Africa. When ready we want to make the map available to the user, as GIS data layers, but also as a web-based map. I am currently trying out OpenLayers to create such a map.

One of the features I want to include is the option for the user to hide/show different vegetation types. You can see an example here (unfortunately it doesn’t work in Internet Explorer for the moment due to some bug I haven’t been able to solve yet). That means I need to create one layer per vegetation type, i.e., I need to split up the the vegetation map according to the vegetation type. Continue reading “Splitting vector maps in QGIS and GRASS GIS”