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Tutorials using the Python API for QGIS (PyQGIS) to automate GIS workflows and analyses with both raster and vector data. QGIS is free, open-source software. The QGIS Python API extends QGIS functionality by creating opportunities to automate and customize workflows and implement new algorithms.
If you’re looking for a way to automate your GIS workflows and products, the QGIS Python API (PyQGIS) may be able to save you a lot of time. With PyQGIS you can write Python code that automates QGIS tasks that range from loading data to creating and saving map layouts. I’ve used PyQGIS to write…
Just as spatial joins can be performed in QGIS with the Join Attributes by Nearest tool, the QGIS Python API (PyQGIS) can be used to perform spatial joins in the same manner. This article will demonstrate, with code, how to perform a spatial join with PyQGIS. This example will join the attributes of a line…
Using attribute fields in calculations is one of the most fundamental components of GIS analysis. Field calculations are what makes it possible to take data linked to spatial features and analyze features based on what they are and where they are. Manually performing field calculations in QGIS can be tedious, especially if you’re working with…
The QGIS Python API (PyQGIS) makes it really simple automate a feature dissolve. PyQGIS gives access to all the QGIS processing tools directly from the Python interface. This tutorial will demonstrate three different dissolve examples with Python in QGIS. Basic Dissolve with Python First, lets dissolve polygon features into a single polygon, this is the…
It is a common need to summarize information from a gridded dataset within an irregularly shaped area. While at first glance this may seem simple, reconciling differences between raster (gridded) and vector (polygon) datatypes can quickly become complicated. This article shows how to implement a zonal statistics algorithm in Python in 4 steps. Load raster…
It is very simple to clip vector layers with PyQGIS. This tutorial will demonstrate how to use Python in QGIS to clip a line layer with a polygon layer. First, import the processing module and set the paths to the line, polygon and output layers. The next step is to run the clip tool. This…
This tutorial will demonstrate how to measure the distance between two geometries in QGIS using Python. First we will measure the distance between points in the same layer. Then we will measure the distance between features in a points layer and a lines layer.
Creating a buffer around features is a common spatial analysis task. This blog post demonstrates how to customize and automate buffer operations with Python in QGIS (PyQGIS).
A common operation with vector layers is to select features based on attribute values and save those features to a new vector layer (i.e. shapefile). This tutorial will walk you through how to create a new shapefile from selected features. We’ll select some features, then save those features to a new shapefile. First, we’ll open…
In this tutorial, we’ll walk through how to create a shapefile from scratch with the QGIS Python (PyQGIS) API. You shouldn’t need to do this, but if you’re running into problems where functions don’t show up you can import the qgis module at the beginning. This usually isn’t a problem but there have been a…
With the PyQGIS API you are able to use Python in QGIS to automate the creation of map layouts. There are two reasons this is really awesome! First, once you’ve written the initial code to set up the map, you can change map symbology or map layers and exactly replicate layout. Second, once you have…
This tutorial will teach you how to render (print or save) a QGIS layer as an image using the PyQGIS Python API. Automating layer rendering can be very useful to create and save visualizations that have consistent styling, extent and format. The first thing you need to do is create a QImage. Here we create…
In a previous tutorial I showed you how to access raster values and data with the Geospatial Data Abstraction Library (GDAL). This tutorial will show you how to create a raster with GDAL. Start by importing the gdal and osr Python modules. The osr module is used for handling spatial references. Also import numpy. Now…
PyQGIS has some methods for accessing single values in a raster, but the best way to access raster data is using the Geospatial Data Abstraction Library, or GDAL. GDAL comes pre-installed on the QGIS Python interpreter, so if you access the Python interpreter from QGIS (Plugins > Python Console) you won’t have to install any…
Deleting features is a common operation in QGIS. It is easy to automate this task with Python, allowing you to quickly delete features based on any conditions you set. First, select the layer from which you want to delete features. This line of code will select the first layer with the name ‘layer name’. You…
Geometry is what defines the shape and spatial location of a feature. Features can be points, lines, or polygons, can be anywhere on earth, and can be represented by coordinates in a number of different units (depending on the coordinate reference system, or projection). Points are represented by a single coordinate pair while lines and…
The QGIS Python API (PyQGIS) makes it possible to automate creation of point features. This tutorial will show you how to add features to an existing shapefile. For this example we will assume the layer containing the point features is already opened in the QGIS table of contents. First, we save all layers with a…
Objectives: Select features from a vector layer Iterate over selected features Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write…
Objectives: Retrieve data from the vector attribute table Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write code in the…
Objectives: Get statistics for a raster band Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write code in the editor…
Objectives: Get information from layers that have already been added to the QGIS interface Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I…
Objectives: Load raster and vector layers without adding them to the QGIS interface Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer…
Objectives: Query the value of a raster layer at a points Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write…
Objectives: Add fields to a shapefile Delete fields from a shapefile Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write…
Objectives Load and symbolize a vector layer with pyqgis Apply basic and graduated symbology Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I…
More information can be found in the PyQGIS Developer Cookbook. Requirements QGIS version 3.0, or greater Objectives Load and symbolize a raster layer with pyqgis Get statistics from a raster band Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into…