QGIS 2.10 Pisa is out!

The new QGIS 2.10 (Pisa) has been released, with many great new features, tweaks and enhancements. Check out the changelog for the highlights (you’ll need some time, it is again an impressive list of improvements and new features).

The source code and binaries for Windows, Debian and Ubuntu are already available via the large download link on the QGIS home page.  More packages will follow as soon as the package maintainers finish their work.

A big thanks to the developers, this is again an impressive piece of work!

Update of r.forestfrag addon for GRASS GIS 7.0

Riitters et al. (2000) proposed a quick approach to measure the degree of forest fragmentation that could be relatively easily implemented and which only required a map with forest and non-forest. Following their approach, Sylla consult created a shell script for GRASS GIS 6.4 to create a raster layer with six categories (non-forest, patch, transitional, edge, perforated, interior and undetermined) as a measure of forest fragmentation. See their blog post with an explanation how the script works or the above-cited article for a more in-depth description.

I adapted the script to make it work on GRASS 7.0, including some further improvements, such as the option to select the size of the moving window, the option to trim the output layer to avoid the edge effect that comes with moving-window calculations and the option to keep intermediate layers.

I have now rewritten the script as a Python addon. See here for the manual page. Continue reading

Locus Map Pro carries its support for MBTiles to the next level

I wrote before about the MBtiles format, a convenient format to store tiled maps in a single portable sqlite database. Probably the easiest way to create them is with Tilemill, as described here. The format is supported by amongst others QGIS, but it is especially suitable for use with map viewers on your mobile device.

The format is now supported by various mobile map viewers, including e.g., Geopaparazzi and OruxMaps. One I like for its rich set of features is Locus Map Pro. I normally only write about open source, but I think the developer of this app deserves some credit for being one of the first (as far as I am aware of) to support the MBtiles format.  Up to very recently you could only view maps in MBtiles format (similar to the other viewers mentioned above), but with the latest update support for the UTFgrid feature has been added.This basically adds interactivity to your map.
Continue reading

Rescale your raster data layer

Sometimes you want to rescale a raster layer, e.g., to reduce the number of categories, or to create a common scale for different raster layers. Very basic of course, so you can expect to find an appropriate function in any self-respecting GIS software. Just be aware that different terms are being used for the same thing, e.g., scale in gdal, rescale in GRASS and normalize in SAGA GIS. Below a few ways to do this using my favourite GIS programs: GRASS GIS, QGIS, SAGA GIS or gdal. Continue reading

Calculating the raster cell area of an unprojected raster layer

What if you get a raster layer with number of people per raster cell, like for example the population layer from Afripop,  and you want to convert it to a population density layer?

Well, obviously, you need to divide the number of people by the surface area of the raster cells. However, the surface area of the raster cells of an unprojected (lat/lon) are not constant; they decrease with increasing latitude. So what you need is a raster layer with the surface areas of the cells.

I thought I had seen a function in GRASS GIS to do this, but that might have been a typical case of the wish being the father to the thought. But anyway, it isn’t terribly difficult to calculate it yourself using the map calculator. Continue reading