![]() ![]() Or in case of a layer input, you’ll be able to select from the layers that are added to your QGIS map currently. ![]() Or if you have a number input you’ll be asked to enter a number. So say you add a file input, then you’ll be able to select which file you want to use for this input. All inputs will later on create a form field that you will be asked to fill in before running the model. ![]() Let’s get processingĪs you can imagine, given the scenario, we need the following two inputs:īefore we define these inputs let’s quickly look into how they work. Usually you would start with some inputs, define what you want to do with the input, and then save it as one or multiple outputs. The white main space, let’s call it workspace, is where you compose your model. If you’ve used the toolbox of QGIS before they will be familiar to you. In the second tab of the column, named algorithms you can find the tools you can use to manipulate the data. This could be simple values such as text or numbers, or also layers and files. In the left hand column you’ll find a window with possible input types into the model. You can access the Graphical Modeler or Processing Modeler through the Menu under Processing > Graphical Modeler. Getting started with the processing modeler Now load the population data GeoTIFF into QGIS (hrsl_tza_pop.tif) - again easiest by dragging and dropping it into QGIS, or alternatively through the menu Layer - Add Layer - Add Raster Layer. Population dataĮxtract the zip file for Tanzania that you have downloaded from the Columbia University page. This step is required because otherwise when working directly on the GeoJSON the projection doesn’t seem to be picked up correctly and hence the process fails to calculate the numbers. Also make sure to name the exported file to something meaningful, like admin_zones You can pick a format of your choice and make sure to leave Add save file to map checked. We will have to export the polygon to a new layer by right-clicking on the layer and then Export > Save Feature as. There will be two layers in the boundaries GeoJSON, one with points, one with polygons. Alternatively you can add it through the menu via Layer - Add layer - Vector Layer. Grab the GeoJSON you have downloaded from the Overpass API and drag it into QGIS. The following steps will explain how to load the data sets into QGIS. to Overpass Turbo query - Click on Run, click continue anyway when a warning comes up, then click Export once processing has finished and Download as GeoJSON OpenStreetMap level 4 administrative boundaries, extracted using the Overpass API. Data typeĭata Download ( Facebook Blog Post about Open Population Datasets )Īdministrative boundaries: Regions of Tanzania For this I need the following data input. You should have some familiarity with how to load and inspect data in QGISĪs a scenario I would like to calculate the population density per region in Tanzania.You need to have a working version of QGIS (preferably 3.x) installed.Getting started with the processing modeler.Towards the end I will discuss potential pitfalls of the tool as well as alternatives. In this post I will walk through the features of the processing modeler using an example scenario. I have only really started using it recently and it is by no means perfect (more on this in the pitfalls section at the bottom) but it is great for what it is built for - repetitive, even complex processing flows, on small to medium sized datasets of relatively simple data. Luckily QGIS comes with a nice tool to help you in these cases. You might set some parameters slightly differently without noticing for example and compare pears with apples. This is not only time-consuming but also prone to errors. Then when you get a new dataset and want to apply the same logic - same procedure. Whether you are a seasoned QGIS user or new to the whole world of GIS you have probably applied a repetitive set of manipulations to your data. Modelling your data processing flow in QGIS
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