GIS AH C8

Module: Plugins

Plugins allow you to extend the functionality QGIS offers. In this module, you'll be shown how to activate and use plugins.

Lesson: Installing and Managing Plugins

To begin using plugins, you need to know how to download, install and activate them. To do this, you will learn how to use the Plugin Installer and Plugin Manager.

The goal for this lesson: To understand and use QGIS' plugin system.

Basic.png Follow along: Managing Plugins

  • To open the Plugin Manager, click on the menu item Plugins \rightarrow Manage Plugins.
  • The following dialogue will open, showing the different plugins already installed in your QGIS software. What you see may differ slightly to the image below, depending upon what plugins you have installed:

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You can activate or deactivate these plugins by clicking on their corresponding check box.

The list of plugins that you can activate and deactivate only draws from the plugins that you currently have installed. To install new plugins, you need to use the Plugin Installer.

Basic.png Follow along: Installing New Plugins

  • To start the Plugin Installer, click on the menu item Plugins \rightarrow Fetch Python Plugins.

A dialogue will appear. The amount of plugins that you see here will differ, depending on your setup.

QGIS plugins are stored online in repositories. By default, only the official repositories are active, meaning that you can only access official plugins. These are usually the first plugins you want, because they have been tested thoroughly and are often included in QGIS by default.

It is possible, however, to try out more plugins than the default ones. To do this:

  • Open the Options tab on the Plugin Installer dialogue:

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  • Click the Show all plugins except those marked as experimental option.

If you want to, you can click on the Show all plugins, even those marked as experimental option. Be aware that experimental plugins may not be fully tested.

  • Now go back to the Plugins tab to find the available plugins.

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  • To install a plugin, simply click on it in the list and then click the Install plugin button.

In conclusion

Installing plugins in QGIS is simple.

What's next?

Next we will introduce you to some useful plugins as examples.

Lesson: Useful QGIS Plugins

Now you can install, enable and disable plugins. Let's see how this can help you in practice by looking at some examples of useful plugins.

The goal for this lesson: To familiarize yourself with the plugin interface and get acquainted with some useful plugins.

Basic.png Follow along: The OpenLayers Plugin

  • Start a new map with only the streets layer in it.
  • Using the Plugin Installer, find the plugin by entering the word Open in the Filter field.
  • Select the Google Layers plugin from the filtered list:

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  • Click the Install plugin button to install.
  • When it's done, close the Plugin Installer.
  • Open the Plugin Manager.
  • Enable the new plugin:

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  • Check the box beside it.
  • Now click OK to enable the plugin.

To use the plugin:

  • Open the plugin by clicking on Plugins \rightarrow Open Layers \rightarrow Settings.
  • Use the dialogue to choose a map type you want. In this example, we'll use the "Add Google Satellite Layer" type map, but you can choose any others if you want.
  • Enable "on the fly" projection and use the Google Mercator projection:

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You should now have a new raster image in from Google that you can use as a backdrop, or to help you find out where you are on the map. Here is such a layer, with our own vector road layer as overlay:

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Moderate.png Follow along: The OpenStreetMap Plugin

Since we're using OpenStreetMap (OSM) data in our examples, it would be instructive to know where it comes from. QGIS has a plugin that allows you to download and edit this kind of data easily.

  • First, ensure that you have the plugin installed by opening the Plugin Installer and filtering on the word street:

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  • The OpenStreetMap plugin should be installed by default, but if it isn't, you can get it by clicking the Install plugin button.
  • Once it's installed, activate it via the Plugin Manager.
  • A new buttons and, if activated in View \rightarrow Panels \rightarrow OSM Feature, a new panel will be added to your interface:

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Let us download data for Bandung. The plugin will download data for the area currently on your map.

  • Zoom in to the Bandung area.
  • To add data, click on the Download OSM data button:

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Note: You may see a message stating that the latitude, longitude, or both extents are too large. This is because the OSM server doesn't have the capacity to continually give people data about the whole world. To prevent people trying to download too much data, there's a limit to the size of the area for which you can download data. If you get one of these error messages, zoom in to a smaller area on the map.

  • If you have an acceptable area, you can leave the other options as default and click the Download button.
  • After a while, the data will be downloaded, and will be shown in your map automatically. Here's an example:

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With any of the OSM layers selected in your Layers list, the buttons in the plugin's dock panel will become active:

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  • Using the plugin's own Identify feature tool (at the far left of the above buttons), click on any feature in the OSM layers to retrieve its data and see it displayed in the plugin interface. For example, clicking on the polygon near the top of the screen in our example shows it is a golf course:

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  • You can create new features (point, lines, polygons) as well as edit a feature that you have identified. For example, using the plugin's Identify feature tool as before, you can click on this polygon and see that it is a forest without a name:

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  • Double-click in the <new tag here> field.
  • Select a new tag (attribute) from a list. Let's choose name:

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  • Double-click in the Value field:

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You can now enter a name for the forest. You can save your changes to the original source data, too. This makes the changes available internationally on the OSM server.

  • Click the Upload OSM data button:

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This gives you a dialogue, which you can fill in as needed.

If you have a user account at OSM, you can enter your credentials in the spaces provided and click the Upload button to save those changes.

Note that the plugin has many other functions: for example, you can also save OSM layers to a local directory, load data from saved OSM layers, and export OSM data as shapefiles.

OSM's data comes from, and is maintained by, the efforts of their users. Contributing data using this plugin allows you to help improve the quality of the OSM data you depend on.

In conclusion

There are many useful plugins available for QGIS. Using the built-in tools for installing and managing these plugins, you can find new plugins and make optimum use of them.

What's next?

Now we will look at combining some of the skills you have learnt in a practical exercise involving data from iSIKHNAS.

Click here to go to Module 9: GIS for Animal Health

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