Automating GIS processes with graphical modeler in QGIS
By: Gispo Ltd.
Tags: Geospatial, Maps, Qgis, GIS

It’s all about saving time, right? QGIS’s graphical modeler can definitely help you out here if you’re a GIS expert wanting to speed up those routinary, personal or collective GIS processes. Without any programming knowledge required, graphical modeler really can help you go through some painless automation and optimization on your GIS processes. Now let’s go through a use case application for using graphical modeler in QGIS for those who are not familiar with this great toolset.

Graphical modeler in action.

So imagine there’s an expert who needs to calculate:

What is the surface area corresponding the extent of the urban tree canopy per administrative units (postcodes) in Melbourne, Australia?

So, first the GIS expert goes on thinking, well first I need to 1) calculate the actual tree canopy extent area for every tree with Field calculator and then 2) make an intersection and sum-up with the Join attributes by location (summary) -tool 3) and finally divide the aggregated tree canopy area with the administrative units surface area information.

City of Melbourne and the canopy polygons

So, the expert goes and implements the plan and finally gets the data out. Nice! Wait a minute, while observing the results, the expert discovers that the tree canopy data ain’t actually the most updated version. Oh! No worries, let’s do the process all over again.

Few weeks after the analysis, the expert shares the results with colleagues, who come to ask: so, how did you do it? “Well…”, the expert starts and goes through the whole process in detail.

The during the following quarter city organization requires the information to be updated with newly captured data. So, here we go again, the expert starts working while feeling confident doing it properly and in time. Nevertheless, the expert forgets what was the tool’s name to get the results on the intersection of the datasets and struggles during a few attempts but finally gets the information altogether, to share the updated results with the persons of interest.

This is common for a lot of GIS experts, right? Well, it just shouldn’t be. If we’d bypass all the previous hassling with a tool called graphical modeler in QGIS, we could implement our GIS processes 1) with fewer quality flaws and 2) without the necessity to remember all the tools 3) besides providing reproducible tools for our repetitive GIS processes.

The finished model.

And this is how the expert could leverage the model file for her/his own processes, or pass it on to someone else, and get some great maps on the aggregated canopy extent area per administrative units from here on.

Of course, you could implement the same use case and a lot more with spatial SQL / Python (/PyQGIS) / R, but I guess that’s another story, for another time — but it’s important to mention it since eventually, our aim should be to build fully reproducible and automated GIS processes.

If you learned something from this blog post, please share or just give a Clap. And if you want to get an in-depth perspective and understanding on leveraging graphical modeler in QGIS for you or your team, we would love to connect with you and make you an offer. You can write us through this from.