QGIS is today one of the most widely used open-source GIS platforms in the world. Its functional richness is impressive, but what really makes it powerful is its extensibility through plugins<\/strong>.<\/p>\n\n\n\n

A QGIS plugin allows you to add custom features: automate repetitive tasks, create tools adapted to a specific profession, test new methods, or simply make daily work easier.<\/p>\n\n\n\n

This tutorial is intentionally aimed at people with limited programming experience<\/strong>. It does not aim to make you a Python expert but to give you the foundations to:<\/p>\n\n\n\n

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understand how a QGIS plugin works,<\/li>\n\n\n\n
modify an existing plugin,<\/li>\n\n\n\n
create your own simple and useful tools.<\/li>\n<\/ul>\n\n\n\n
The goal is to learn just enough Python and QGIS architecture<\/strong> to become autonomous.<\/p>\n\n\n\n
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<\/span>Why Develop Your Own QGIS Plugins?<\/span><\/h2>\n\n\n\n
<\/span>Automate Repetitive Tasks<\/span><\/h3>\n\n\n\n
If you use QGIS often, you have probably repeated the same steps several times:<\/p>\n\n\n\n
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loading layers,<\/li>\n\n\n\n
applying styles,<\/li>\n\n\n\n
running a series of processes,<\/li>\n\n\n\n
exporting results.<\/li>\n<\/ul>\n\n\n\n
A plugin can group these actions under a single button<\/strong>.<\/p>\n\n\n\n
<\/span>Adapt QGIS to Your Workflow<\/span><\/h3>\n\n\n\n
The needs of a GIS professional, teacher, government agent, or researcher are not always covered by standard tools. A plugin can integrate:<\/p>\n\n\n\n
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business rules,<\/li>\n\n\n\n
consistency checks,<\/li>\n\n\n\n
specific calculations.<\/li>\n<\/ul>\n\n\n\n
<\/span>Learn Programming Gradually<\/span><\/h3>\n\n\n\n
Developing a QGIS plugin is an excellent way to get started with Python:<\/p>\n\n\n\n
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the results are concrete and visual,<\/li>\n\n\n\n
errors are often easy to identify,<\/li>\n\n\n\n
progress can be made in small, manageable steps.<\/li>\n<\/ul>\n\n\n\n
<\/span>Share (or Keep for Yourself)<\/span><\/h3>\n\n\n\n
A plugin can remain strictly personal, be shared within a team, or be published publicly through the official QGIS repository.<\/p>\n\n\n\n
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<\/span>What Does a QGIS Plugin Consist Of?<\/span><\/h2>\n\n\n\n
A QGIS plugin is primarily a folder containing several files<\/strong>, each with a specific role. The good news: you do not need to understand everything in depth right away.<\/p>\n\n\n\n
Here\u2019s the minimal structure of a plugin<\/strong>:<\/p>\n\n\n\n
MyPlugin\/\n\u251c\u2500\u2500 __init__.py\n\u251c\u2500\u2500 metadata.txt\n\u251c\u2500\u2500 my_plugin.py\n\u2514\u2500\u2500 resources.qrc (optional)\n<\/code><\/pre>\n\n\n\nWe will go through these files one by one.<\/p>\n\n\n\n \n\n\n\n<\/span>The __init__.py<\/code> File<\/span><\/h3>\n\n\n\nThis is the entry point of the plugin<\/strong>.<\/p>\n\n\n\n Its main role is to tell QGIS which Python class should be loaded when the plugin is activated.<\/p>\n\n\n\n Simplified example:<\/p>\n\n\n <\/div><\/div><\/div><\/div><\/p>\n\n\n\ndef classFactory(iface):\n from .my_plugin import MyPlugin\n return MyPlugin(iface)\n<\/code><\/pre>\n\n\n<\/div><\/div>\n\n\n\n At this stage, remember that:<\/p>\n\n\n\n \nthis file is mandatory<\/strong>,<\/li>\n\n\n\n it links QGIS to your main code<\/strong>.<\/li>\n<\/ul>\n\n\n\n<\/span>Line-by-Line Explanation<\/span><\/h4>\n\n\n\n1️⃣ def classFactory(iface):<\/code><\/p>\n\n\n\n ✔ QGIS requires<\/strong> a function with this exact name: classFactory<\/code>.<\/p>\n\n\n\n When QGIS loads your plugin, it automatically calls:<\/p>\n\n\n <\/div><\/div><\/div><\/div><\/p>\n\n\n\nclassFactory(iface)\n<\/code><\/pre>\n\n\n<\/div><\/div>\n\n\n\n and passes:<\/p>\n\n\n\n \niface<\/code> = the QGIS interface object (QgisInterface<\/code>)<\/li>\n<\/ul>\n\n\n\nThis object gives access to:<\/p>\n\n\n\n \nthe map canvas,<\/li>\n\n\n\n the Plugins menu,<\/li>\n\n\n\n the toolbar,<\/li>\n\n\n\n the active layer,<\/li>\n\n\n\n messages\/logs,<\/li>\n\n\n\n etc.<\/li>\n<\/ul>\n\n\n\n➡️ This is the central object that allows a plugin to interact with QGIS.<\/p>\n\n\n\n \n\n\n\n2️⃣ from .my_plugin import MyPlugin<\/code><\/p>\n\n\n\n The dot (.<\/code>) means: \u00ab\u00a0from the same folder as this file\u00a0\u00bb.<\/p>\n\n\n\n QGIS loads the main class from:<\/p>\n\n\n\n my_plugin.py\n<\/code><\/pre>\n\n\n\nThis class contains:<\/p>\n\n\n\n \ninitGui()<\/code> \u2192 adds actions, menus, icons<\/li>\n\n\n\n unload()<\/code> \u2192 removes plugin elements<\/li>\n\n\n\n business functions (tool activation, window display, etc.)<\/li>\n<\/ul>\n\n\n\n➡️ This is the root class<\/strong> of the plugin, controlling everything.<\/p>\n\n\n\n \n\n\n\n3️⃣ return MyPlugin(iface)<\/code><\/p>\n\n\n\n QGIS expects an instance<\/strong> of the class, not the class itself.<\/p>\n\n\n\n So we:<\/p>\n\n\n\n \ninstantiate MyPlugin<\/code>,<\/li>\n\n\n\n pass it the QGIS interface (iface<\/code>).<\/li>\n<\/ul>\n\n\n\nQGIS will then:<\/p>\n\n\n\n \ncall initGui()<\/code> when activating the plugin,<\/li>\n\n\n\n call unload()<\/code> when deactivating.<\/li>\n<\/ul>\n\n\n\n➡️ This is the concrete creation of the plugin<\/strong> in QGIS.<\/p>\n\n\n\n \n\n\n\n<\/span>Summary<\/span><\/h3>\n\n\n\n\n__init__.py<\/code> tells QGIS which class to use for the plugin.<\/li>\n\n\n\n The classFactory()<\/code> function is mandatory<\/strong>.<\/li>\n\n\n\n iface<\/code> provides full access to the QGIS interface.<\/li>\n\n\n\n The plugin starts functioning only after instantiating:<\/li>\n<\/ul>\n\n\n\nMyPlugin(iface)\n<\/code><\/pre>\n\n\n\n \n\n\n\n<\/span>The metadata.txt<\/code> File<\/span><\/h3>\n\n\n\nThis file is fundamental<\/strong>: without it, QGIS will not recognize the plugin.<\/p>\n\n\n\n It contains general information:<\/p>\n\n\n\n \nplugin name,<\/li>\n\n\n\n description,<\/li>\n\n\n\n author,<\/li>\n\n\n\n version,<\/li>\n\n\n\n minimum QGIS version.<\/li>\n<\/ul>\n\n\n\nExample:<\/p>\n\n\n <\/div><\/div><\/div><\/div><\/p>\n\n\n\n[general]\nname=My First Plugin\ndescription=A simple plugin to learn\nversion=0.1\nauthor=Your Name\nqgisMinimumVersion=3.16\n<\/code><\/pre>\n\n\n<\/div><\/div>\n\n\n\n This file is what appears in the QGIS Plugin Manager<\/strong>.<\/p>\n\n\n\n \n\n\n\n<\/span>The Main Python File (e.g., my_plugin.py<\/code>)<\/span><\/h3>\n\n\n\nThis is where the core of the plugin<\/strong> resides.<\/p>\n\n\n\n It typically contains:<\/p>\n\n\n\n \nthe main plugin class,<\/li>\n\n\n\n the initGui()<\/code> and unload()<\/code> methods,<\/li>\n\n\n\n the code that adds a button or menu in QGIS.<\/li>\n<\/ul>\n\n\n\nSimplified example:<\/p>\n\n\n <\/div><\/div><\/div><\/div><\/p>\n\n\n\nclass MyPlugin:\n def __init__(self, iface):\n self.iface = iface\n\n def initGui(self):\n pass\n\n def unload(self):\n pass\n<\/code><\/pre>\n\n\n<\/div><\/div>\n\n\n\n Don\u2019t worry if this seems confusing\u2014each element will be explained in detail in future articles.<\/p>\n\n\n\n \n\n\n\n<\/span>Optional but Common Files<\/span><\/h3>\n\n\n\n<\/span>Graphical Interfaces (.ui<\/code>)<\/span><\/h4>\n\n\n\nQGIS uses Qt for GUIs. .ui<\/code> files are created with Qt Designer<\/strong>, without coding.<\/p>\n\n\n\n They allow you to build windows with:<\/p>\n\n\n\n \nbuttons,<\/li>\n\n\n\n dropdown lists,<\/li>\n\n\n\n input fields.<\/li>\n<\/ul>\n\n\n\n<\/span>Resources (resources.qrc<\/code>)<\/span><\/h4>\n\n\n\nThis file collects:<\/p>\n\n\n\n \nicons,<\/li>\n\n\n\n images,<\/li>\n\n\n\n other graphical resources.<\/li>\n<\/ul>\n\n\n\nIt is compiled into Python so it can be used in the plugin.<\/p>\n\n\n\n \n\n\n\n<\/span>What You Need to Remember for Now<\/span><\/h3>\n\n\n\nAt this stage, the key points are:<\/p>\n\n\n\n \na QGIS plugin is a file structure<\/strong>, not a big complex program,<\/li>\n\n\n\n each file has a specific role<\/strong>,<\/li>\n\n\n\n you can create simple, useful plugins<\/strong> with very little code.<\/li>\n<\/ul>\n\n\n\n \n\n\n\n<\/span>What\u2019s Next?<\/span><\/h3>\n\n\n\nIn the next article, we will see:<\/p>\n\n\n\n \nhow to create an empty plugin<\/strong> using Plugin Builder,<\/li>\n\n\n\n where to place the files,<\/li>\n\n\n\n how to load and test the plugin in QGIS<\/strong>.<\/li>\n<\/ul>\n\n\n\nThe goal will be to have a first functional plugin<\/strong>, even if it doesn\u2019t do much yet.<\/p>\n\n\n\n 👉 The most important thing is not to go fast, but to understand each step<\/strong>.<\/p>\n\n\n\n \n\n\n\n<\/p>\n","protected":false},"excerpt":{"rendered":" Developing a QGIS plugin may seem reserved for experienced programmers, but with the right approach, anyone can create their own. 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