Creating Vector layer from selected features with PyQGIS

Slicing and Dicing GIS Data: How to Create Vector Layers from Selected Features with PyQGIS

Ever felt like you’re drowning in GIS data? You’ve got this massive dataset, but you only need a tiny, specific piece of it. Maybe you’re after all the parcels zoned for commercial use, or perhaps just the highways classified as “scenic routes.” Manually carving out these selections? Forget about it! That’s where PyQGIS, the Python superpower for QGIS, comes to the rescue. It lets you automate the whole process of creating new vector layers from just the features you want. Trust me, it’s a game-changer.

Why Bother? The Real-World Need

Think about it: GIS projects often demand laser-like focus. You need to isolate stuff. I remember one project where I had to analyze traffic patterns only around schools. Extracting those specific road segments from the city’s entire road network manually? Ugh, no thanks! PyQGIS lets you script these extractions, saving you tons of time and preventing those oh-so-common human errors.

Okay, How Do We Do It? The PyQGIS Toolkit

There are a few cool ways to tackle this with PyQGIS, each with its own little quirks and best uses. Let’s dive in.

1. The QgsVectorFileWriter.writeAsVectorFormat() Power Move

This is your direct route to creating a brand-new vector file, like a shapefile. It’s like saying, “Hey, take these features and save them right here.” You get to control everything – the file type, how the characters are encoded, the whole shebang.

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