Blog Nederlandse QGIS gebruikerscommunity

A short post in Dutch, to let us dutchies know of a new version of the ‘PDOK services plugin’ which eases the use of our national OWS services.
If you want you can install it, and for example view the different soli types of The Netherlands:

Another nice service is the 25cm Aerial Map of The Netherlands (Luchtfoto 2016 Ortho 25cm RGB).
Happy QGIS’ing all!

How to visualize point data with Z values? Let’s say: we have data about noise pollution in multi-storey buildings. The point data (apartments) looks like this:
The attribute table looks like this:
We see X and Y coordinates, and a Z (height) value. The DB column gives the actual noise data, which we want to visualize. How to do this?
One idea was to use diagrams. QGIS, however, gives only pie charts and histograms, which don’t satisfy in my case.
Another idea was the Point Displacement option in the styling of the layer. This didn’t work out well either, because I couldn’t arrange the points properly. I wanted to place them above each other, with the highest Z value on top.
The idea that did work out was to use Offset X,Y in the Symbol selector:
Using this, you can offset the marker symbols in horizontal (X) and vertical (Y) direction. Instead of just using X and Y values, you can also use an expression. Using an expression, you get the possibility to use values in the attribute table for changing the X and Y offset value for each point. That gave me the solution!
After a lot of trying I used this expression:
‘0, ‘|| to_string(-1 * “z”)
Let me explain. “z” is the height value I want to use. A positive Z value gives the marker a downward offset. I want it upward, so I took the negative of Z. Because the result of the expression has to be a string value, I used the to_string expression to do so. Because the expression changes both X and Y, and I didn’t want to change the X value, I used ‘0, ‘ in the beginning of the expression, and concatenated (||) the 2 expressions.
Here’s the result:
Now you see all apartments in the different blocks: the markers at the bottom are the lowest in the block, at the top are the highest apartments. There are some gaps, because the data were incomplete. The small blue points indicate the original X and Y coordinates.
The possibilities of these expressions are myriad. And with adding text labels, you can use these expressions too, to place them exactly where you want (in the markers, beside the markers, whatever).
Good luck!

Sorry, this entry is only available in Dutch.

Sometimes I prefer to publish my map in gray instead of black. But all newly added QGIS composer items are set to black by default.

For changing the colors more easily and rapidly I created the “Turn Gray” plugin. By default it changes all foreground colors (labels and outlines) to gray. But you are free to choose more cheerful colors too. And for the background as well.
Right now not all composer items are supported, but the map, legend, labels and scale bar do. Tables, arrows and map grids will have to wait.
I hope others will be happy to use this tool as well, that’s the idea behind open source!
Here some examples:

Sorry, this entry is only available in Dutch.

Sorry, this entry is only available in Dutch.