24: Clipping the Census Small Area vector polygons [C-grades and above]#
You now have a vector polygon map layer of the 2022 Census small areas - but much like the rivers, lakes, and other data, this layer has data for the entire State. You certainly don’t need that - but we can do what we did for the other vector layers, and clip the layer to show only the area we want.
Processing the Data#
First, it will speed things up immensely if you toggle off the visibility of the census small areas polygons layer. QGIS will be using quite a lot of computer resources to keep drawing the polygons on the map canvas. We don’t need that, so let’s not waste the resources.
From the menu, choose Vector > Geoprocessing Tools > Clip.
In the Clip window, choose your census vector polygon layer as the Input layer, and your AOI [C-grades] or buffer [B-grades and above] as the Overlay layer.
What this will do is create a new layer, which contains only the census features which are within your AOI or buffer.
Click then Run. When it’s finished, click Close. You should see the new Clipped scratch layer in the Layers panel. We need to save this layer properly.
Right click on the Clipped layer in the Layers panel, and choose Export > Save Features As.
In the Save Vector Layer as… window, make sure Format is set to Geopackage, and CRS is set to EPSG:2157 IRENET95 / Irish Transverse Mercator.
Click the Browse […] button beside File name. In the Save Layer as… window, navigate to your GY4006 folder and SAPS subfolder, type census as the File name, and click Save.
Back in the Save Vector Layer as… window, type Small Areas as the Layer name, and ensure Add saved file to map is selected. Click OK to save and add the new layer.
You should now see the new Census layer in the Layers panel. Remove the original census vector polygon layer and the Clipped scratch layer - you don’t need these anymore, and they’re hogging resources.
Save the project before continuing.