Welcome to this tutorial on Digitizing Map Data in QGIS.
In this tutorial, we will learn to- Create and digitize Point and Polygon shape files.
Change style and color for Point and Polygon features.
To record this tutorial I am using- Ubuntu Linux OS version 16.04 QGIS version 2.18
To follow this tutorial, you should be familiar with basic GIS and QGIS interface.
Digitizing is the process by which, coordinates from a map, image or other sources of data are converted into a digital format.
The converted data can be stored as a point, line or a polygon feature in GIS.
To practise this tutorial, you need to download the thematic map of Bangalore city given in the Code files link.
This is a map depicting development of Bangalore city.
Steps to download the code files.
Click on the link Code files, located below the player and save it in your folder.
Extract the downloaded zip file.
Locate Bangalore.jpg file in the extracted folder.
I have already downloaded the Code file, extracted and saved in a folder on Desktop.
Double-click on the folder to open it.
Right-click on Bangalore.jpg file.
From the context menu select, Open with QGIS Desktop.
QGIS interface opens.
QGIS Tips dialog-box opens. Click on OK button.
Coordinate Reference System Selector dialog-box opens.
Under the heading, Coordinate reference systems of the world, Select WGS 84.
Note that WGS 84 is the most widely used geographic coordinate system.
Click on OK button at the bottom of the dialog-box.
Thematic map of Bangalore is displayed on the canvas.
Now let us create new shape file layers.
Click on Layer menu on the menu bar and select Create Layer option.
From the sub-menu, select New Shapefile Layer option.
New Shapefile Layer window opens.
Here you can see options for 3 types of features, Point, Line and Polygon.
By default Point option is selected. Leave it as such.
Let the CRS be WGS 84.
Click on OK button at the bottom-right corner of the window.
Save Layer as.. dialog-box opens.
Let us name the file as Point-1.
Select a suitable location to save the file. I will choose Desktop.
Click on Save button at the bottom-right corner of the dialog-box.
Files will be saved on the desktop as shown here.
Back to the QGIS interface.
Notice that the file will be automatically loaded in the Layers Panel.
On this map, we will mark the locations where IT departments are established.
Refer to the legend at the bottom-right corner of the map for IT establishments.
IT establishments are indicated as flag symbol.
Locate the points indicating IT establishments on the map.
There are two points indicating IT establishments.
To edit or modify features on the map, we need to select the Toggle editing tool.
Toggle Editing tool is available on the top-left corner of the tool bar.
Click on the Toggle Editing tool to select it.
Click on Add Feature tool on the tool bar.
The cursor is now displayed as a crosshair icon.
Click on IT establishment symbol on the map.
An input-box Point-1 Feature Attributes opens.
Type 1 in the id text box. Click on OK button.
Similarly click on the second IT establishment and save the feature as 2. Click on OK button.
Now to stop editing, again click on Toggle Editing tool on the tool bar.
Stop editing dialog-box opens.
Click on Save button.
Observe, on the map, two colored point features are created.
We can check the two features created, by opening the attribute table.
Right-click on the Point-1 layer on the Layers panel.
From the context menu, select Open Attribute Table option.
In the Point-1: Features dialog-box, in id column, two points are created.
Close the attribute table dialog-box.
Style and color of these point features can be changed for clear visibility.
Right-click on the Point-1 layer.
From the context menu choose Properties option.
Layer Properties dialog-box opens.
Click on the Color drop down.
Choose a color by rotating the color triangle.
Increase the size by clicking on upward arrow triangle at the end of Size text box.
Click on OK button at the bottom of the dialog-box.
Notice the change in color and size for the Point features.
Now let us create a shape file containing Polygon features.
Click on Layer menu on the menu bar. Select Create Layer option.
From the sub-menu, select New Shapefile Layer.
New Shape File Layer window opens.
Select Type as Polygon.
In the New field Name text box, type area.
Let the Type be Text data.
Click on Add to fields list button
In the Fields List table, you will see area row added. Click on OK button.
Save layer as.. dialog-box opens.
Type the File name as Area-1.
Select a suitable location.
I will select Desktop. Click on Save button.
Notice that Area-1 layer is added to the Layers panel.
We will mark the boundary of Corporation Area and Greater Bangalore area.
Refer to the Legend on the map to locate Corporation area and Greater Bangalore area.
Turn on the toggle editing by clicking on Toggle Editing tool on the tool bar.
Click on Add Feature tool from the tool bar.
Bring the cursor to the map.
To mark the area, click anywhere on the boundary of Corporation area.
Keep clicking on the boundary.
Warning messages may appear at the top of the canvas if the line segments intersect. Please ignore these messages.
If you make a mistake and want to restart the marking process, press Esc Key on the keyboard.
You can start the process again.
Keep clicking on the boundary till you span the entire boundary.
Once you have marked the entire boundary, right-click to end the polygon.
Area-1- Feature Attributes input box opens.
Type 1 in the id text box.
Type Corporation Area in area text box.
Click on OK button.
Observe, on the map new polygon feature is created.
Now we will digitize Greater Bangalore region in the map.
Click on the boundary to digitize Greater Bangalore region as shown here.
After you finish digitizing, right-click to end the polygon.
In the Area-1 Feature Attributes text box, type 2 in the id text box. And Greater Bangalore in the area text box.
Click on OK button.
Again click on Toggle Editing tool in the tool bar to stop editing.
Click on Save button in the Stop editing dialog box.
Right click on Area-1 layer to open attribute table.
Select Open Attribute Table from the context menu.
We can see that 2 features have been created with columns id and area type. Close the attribute table.
We can see that two polygon features have been created.
To change the color and style of polygon feature, right click on Area-1 layer. Select Properties option.
In the Layer Properties dialog-box, select Style option from the left panel.
On the top left corner of the drop down menu, select categorized.
In the column drop down select id. Click on Classify button.
Move the Layer transparency slider to 50 %.
Click on OK button at the bottom of the dialog-box.
Now on the map, we can see that the two Polygon features are in different color.
Details about labeling the features, will be discussed in upcoming tutorials in the series.
Let's summarize.
In this tutorial we have learnt to, Create and digitize Point and Polygon shape files.
Change style and color for Point and Polygon features.
As an Assignment, On the Banglaore thematic map (Bangalore.jpg), Digitize Industrial Estates Digitize the roads on the map, by creating a Polyline feature.
Your completed assignment should look as shown here.
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This tutorial is contributed by Prajwal.M from Sahyadri college of Engineering and Snehalatha from IIT Bombay. Thank you for joining.