Introductory Training On QGIS

What is QGIS?

QGIS (previously known as Quantum GIS) is open-source desktop geographic information system (GIS) application that provides data viewing, editing, and analysis.

Similar to other software GIS systems, QGIS allows users to create maps with many layers using different map projections. QGIS allows maps to be composed of raster or vector layers.

Typical for this kind of software, the vector data is stored as either point, line, or polygon-feature. Different kinds of raster images are supported, and the software can perform image georeferencing, spatial data analysis along with support of various remote sensing tools and models. 

Training Contents

-              Getting Started with QGIS

-              QGIS Plugins

-              Adding and Modifying Vector Layers

-              Viewing data and Vector Attributes

-              Saving your QGIS Projects

-              Using Plugins

-              Adding Raster Images

-              Creating a Map with Print Composer

Software

-              QGIS

Data Set

-              CA_projected.shp

-              CA_Cities_Top10.shp

-              Yosemite_boundary.shp

Image by Mojca JJ from Pixabay

Getting Started with QGIS

•             Open QGIS

Mac: from your Desktop icon or your Applications folder. 

Windows: from your Desktop icon or your Program start.

The QGIS interface has multiple elements outlined here, Take a look at each of the elements:

1.   Layers List/Browser Panel

This will display all the layers you have in the map. You can right click on each layer file for more information and to perform specific functions. You can also expand and collapse items within the panel

2.   Toolbars

The tools you use most often can be displayed here. You can modify which tools are displayed by click on “View­‐> “Toolbars”. You can also move tools around within this toolbar

3.   Map Canvas (where map is displayed)

4.   Status Bar

This shows current information about the map and allows you to adjust the scale.

5. Here you can add in different types of data layers. Note: if you hover over any of these icons, it will display the function name. Explore the available functions.

See the figure next

Image taken from QGIS Desktop version 

QGIS Plugins

Plugins are optional tools that you can import into your QGIS for additional functionality. A useful plugin for QGIS is Open Layers and includes Google Maps, OpenStreetmap and Yahoo Map layers.

•  From the Plugins menu in QGIS, choose Manage and Install Plugins enter Open layers in the search field and select Open Layers Plugin from the list.

 

OpenLayers Plugin

OpenLayers Plugin 

Click the Install plugin button. This will download the plugin from the repository, install it, and load it into QGIS.

Install the Semi-Automatic Classification Plugin. This is a useful plugin for many types of raster operations such as classifications.

Press OK for Welcome Screen 

 Adding and Modifying Vector Layers

 Click on the Add Vector Layer icon 

Add Vector layer icon 

 A screen as shown below appears

Add Vector Layer Dialogue 

Next to Data set click on the Browse button and find the Shapefile called CA_projected.shp. Click Open to add it to the map. The layer will be added to the map and you should see an outline of the state of California. The color may not be aesthetically pleasing, so we can change that.

Added File 

Right click on the CA_projected file in the Layers Panel, then click on Properties. This should automatically take you to the Style panel and there you can change the color, transparency, etc. Click Apply at the bottom. You will see the fill change colors. Click OK.

Layer Styling 

Repeat the previous steps to add the CA_Cities_Top10.shp and Yosemite_boundary.shp files. These are a point file of the ten largest cities in California based on population, and the boundary of Yosemite National Park.

Right click on the CA_Cities_Top10 file in the Layers Panel, then click on Properties. In the Style tab, change the symbol to the city option in the box on the right. Then, using the drop-down menu next to Color, change the fill color to blue.

You can also add labels to a map and modify them based on your specific cartographic needs. Click on the Labels tab. In the top drop down menu choose Show Labels for this Layer. In the drop down menu next to Label With select NAMELSAD. Click Apply.

Image Changing Labels 

Without closing the Properties box, take a look at the city labels in the map.

You can also change the formatting of the labels. Click on the Buffer option within the Labels tab.

Check the Draw text buffer button and keep everything as default. Click on the Shadow option and check the Draw drop shadow. Finally, click on the Placement option and increase the distance to 1 millimeter by clicking on the “up” arrow next to Distance. Click Apply again and close the Properties window. Take a look at the labels again in the map. They are now a bit easier to read.

Image Editing Label Properties 

You can also modify and label the Yosemite layer in the same way. Open the Properties box and change the color to dark green. Click on Simple Fill in the fill box on the left side. Then change the Fill color to green and the Boarder to red.

Label the layer using the UNIT_NAME and give it a white Buffer of 0.7 millimeters.

Viewing Data & Vector Attributes

Using some of the tools on the top of your QGIS project panel, you can modify the view of your data. Click on the Zoom Full  tool. This should display the full extent of all of your map layers. You can also zoom into specific layers. Click on the Yosemite_boundary layer, then click on the Zoom to Layer tool. This should allow you to view the full extent of the Yosemite NPS boundary. You can also zoom to a specific layer by right clicking on the layer in the Layers Panel and clicking on Zoom to Layer.

Zooming Tool 

You can also obtain more information about the specifics of a vector layer by taking a look at the Attribute table.

Right click on the CA_Cities_Top10 layer and click on Open Attribute Table. Here you will see the latitude and longitude of each point, the state, and the city name.

Adding Attribute Layer

Saving your QGIS Projects

It is also very important to save your QGIS projects along the way so that you do not loose any important processing steps. At the top of your screen click on Project, then Save As. Navigate to your data folder for this training and save the project.

Using Plugins

You can also add some background imagery to your map using the Open Layers Plugin. At the top of your screen click on Web, then Open Layers Plugin, then Google Maps, and Google Satellite. It may take some time to load in your map, so be patient! Then zoom to your CA_Projected layer.

 

Adding Plugin

The above and below figure explains the steps

Move the Google Satellite layer to the bottom of the Layers Panel by clicking on Google Satellite and dragging it down below the other layers.

You can then adjust the transparency of the California layer. Right click on the CA_Projected layer and go to Properties. In the Style tab under Layer rendering you can adjust the Layer transparency by sliding the circle to the right or typing in a specific transparency on the box on the right. Adjust the transparency to 40. Click Apply then click OK. Now you can see some of the earth features under the California layer.

As you may have noticed, the Google Satellite layer causes QGIS to run quite slow and can sometimes cause it to freeze. Here is where that regular saving comes in handy! So if you are creating a map it is recommended that you add this layer at the very end of your work. Right click on the Google Satellite layer and click on Remove

   

Adding Raster Images

Click on Add Raster Button

Browse to Calaveras Image in data directory

Select Open

Right click newly added Calaveras layer and select properties

Explore number of bands and other options in properties tab

  Creating a Map with Print Composer 

The Print Composer function allows you to create a map as a PDF or an image file. You can add all the “pieces” of a map such as adding a legend, scale bar, north arrow, etc. Once you create your first map, you can also save the map template for quick map-­‐making in the future. Let’s briefly explore this tool.

Turn off the raster layer by unchecking the layer in the Layers Panel.

At the top of your screen click on Web, then OpenLayers Plugin, then Google Maps, and Google Satellite. It may take some time to load in your map, so be patient! Then zoom to your CA_Projected layer.

Map Composer 

At the top of your screen, click on Project, then New Print Composer. In the name prompt, type Map.

A new window will appear. Under Page size on the right side, change the

Orientation to Portrait.

On the left hand side of the Print Composer, click on Add new map .

Then hover over the blank page and draw a rectangle about the size of your

Page. This will automatically display your project properties within the new map.

If California is not centered, click on Move item content . Then click on the map to move around the contents.

Print Composer 

Click on Add scale bar.

Then click on the lower left side of the map. The scale bar will automatically be displayed. On the right side panel click on Item properties as shown in figure below.

 You can then check out all the other features of the Print Composer. You can style your maps to fit your cartographic needs. To end this homework we will save the map as a pdf.

At the top of your screen, click on Composer, then Export As PDF.

Exporting Map

A screen may pop up saying that it is recommended to print as raster, if so, click OK. This will still have the map as a PDF. Navigate to your webinar folder, name your map Week 1 Map, and click Save. You can then open this file and take a look at the map you created.