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QGIS Python Programming Cookbook, Second Edition

You're reading from   QGIS Python Programming Cookbook, Second Edition Automating geospatial development

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Product type Paperback
Published in Mar 2017
Publisher Packt
ISBN-13 9781787124837
Length 464 pages
Edition 2nd Edition
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Author (1):
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Joel Lawhead Joel Lawhead
Author Profile Icon Joel Lawhead
Joel Lawhead
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Toc

Table of Contents (10) Chapters Close

Preface 1. Automating QGIS FREE CHAPTER 2. Querying Vector Data 3. Editing Vector Data 4. Using Raster Data 5. Creating Dynamic Maps 6. Composing Static Maps 7. Interacting with the User 8. QGIS Workflows 9. Other Tips and Tricks

Change map layer transparency

Map layer transparency allows you to change the opacity of a layer, so the items behind it are visible to some degree. A common technique is to make a vector layer polygon partially transparent in order to allow the underlying imagery or elevation data to add texture to the data.

Getting ready

In a directory called ms, in your qgis_data directory, download and extract the following shapefile from

https://github.com/GeospatialPython/Learn/raw/master/Mississippi.zip.

How to do it...

The process is extremely simple. Transparency is just a method:

  1. First, we load the shapefile layer:
            lyr = QgsVectorLayer("/qgis_data/ms/mississippi.shp",
                                 "Mississippi", "ogr") 
    
  2. Next, we set the layer's transparency to 50 percent:
            lyr.setLayerTransparency(50) 
    
  3. Finally, we add this layer to the map:
            QgsMapLayerRegistry.instance().addMapLayer(lyr) 
    

How it works...

If you set the transparency to 100 percent...

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