Pyqgis

TL;DR: If your QGIS buffer is the wrong size, your CRS is EPSG:4326 (degrees) — switch to a projected CRS (e.g. a local UTM zone) before buffering, or enable the Geodesic Distance option in the QGIS 3.28+ Buffer dialog. The QGIS Buffer tool has one requirement that is easy to miss: the distance you enter is in the unit of the layer’s CRS, not the unit of your project CRS, and not any intuitive real-world unit you might have in mind. ...

Most GIS analysts who try to learn scripting open a blank Python console, type from qgis.core import *, and close the console within ten minutes. PyQGIS documentation dumps you into an object model of two hundred classes with no hint of which ones matter for the three workflows you actually run every week. It is the wrong entry point. The Model Designer is the right entry point. You already use it to wire up Clip, Reproject, and Extract by Location into a reusable graph. The menu option that nobody talks about is one click away: Export → Export as Python Algorithm. QGIS writes a complete QgsProcessingAlgorithm subclass that reproduces your model exactly, including every processing.run() call with the correct parameter dictionary. You now have a working script to modify instead of a blank console to fight. ...