View source for QGIS/C4/Create-Contour-Lines/English


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|| '''Visual Cue'''
||'''Narration'''
|-
|| '''Slide Number 1'''

'''Title Slide'''
|| Welcome to this tutorial on '''Create Contour Lines''' in '''QGIS'''.
|-
|| '''Slide Number 2'''

'''Learning Objectives'''

|| In this tutorial, we will learn to,
* Clip the area in '''DEM''' using the '''Clipper''' tool.

* Show '''contour''' lines for the '''DEM'''.

* And mark the highest elevated area on the '''contour '''map.

|-
|| '''Slide Number 3'''

'''System Requirement'''
|| Here I am using

*'''Ubuntu Linux '''OS version 16.04

*QGIS version 2.18

*And a working Internet connection.

|-
|| '''Slide Number 4'''

'''Pre-requisites'''
|| To follow this tutorial you should be familiar with '''QGIS''' interface.

For the prerequisite tutorials in this series please visit this website.

|-
|| '''Slide Number 5'''

'''Example file'''
||'''DEM''' data required to practise this tutorial is provided in the '''Code files''' link.

Please download and extract the contents of the folder.

|-
|| Cursor on the code files folder.

Double-click on the folder.
||I have saved this folder on the '''Desktop'''. 

Double-click on the folder to open it. 

|-
|| Right-click on '''srtm_51_09.tif '''file and open with '''QGIS''' Desktop.
|| Right-click on '''srtm.tif''' file and select '''Open with QGIS Desktop'''.

The map opens on the screen.

|-
|| Click on '''layer '''on the '''menu bar'''.

Click on '''Add Layer'''.

Click on '''Add Raster layer'''.

|| You can also open the '''tif '''file using '''Add Raster Layer '''option in '''Layer''' menu.

|-
|| Point to the DEM on canvas.
|| On the canvas you will see '''DEM''' of the terrain.

|-
|| Click on '''Raster menu >>Extraction>>Contour'''.
||'''Contour lines''' for this '''DEM''' can be generated using '''Contour tool''' in '''Raster menu'''.

|-
|| '''Slide Number 6'''

'''About Contour lines'''

It is a line on a map joining points of equal height above or below sea level.

This will help us to determine the highest and least elevated areas on the map.
||About '''Contour lines'''.

It is a line on a map joining points of equal height above or below sea level.

This will help us to determine the highest and least elevated areas on the map.

|-
|| Cursor on the map on '''QGIS''' interface.
||We can draw contour lines for the selected area on this map.

|-
|| Click on '''Raster menu>>Extraction>>Clipper'''.
||We will use the '''Clipper''' tool in the '''Raster''' menu to clip the area.

|-
|| Click on the menu item '''Raster'''.

Select '''Extraction''' from drop down.

Select '''Clipper'''.
||Click on the '''Raster '''menu.

Click on '''Extraction''' from drop-down.

Click on '''Clipper'''.

|-
|| Cursor on '''Clipper''' dialog-box.
||'''Clipper''' dialog-box opens.

|-
|| Cursor on '''Input file '''field.
||Select '''Input file''' as the '''DEM''' layer.

Here, by default this layer is already selected.

|-
|| Click on '''Select''' button next to '''Output file '''field.
||Click on '''Select''' button for '''Output file'''.

|-
|| Point to '''Select the raster file to save the results to''' dialog box.

In the dialog-box, name the file as '''Clip-DEM.tif'''. 

Click on '''Save '''button.
||'''Select the raster file to save the results to''' dialog-box opens.

In the dialog-box, name the file as  '''Clip-DEM.tif'''.

Click on '''Save '''button at the bottom right corner.

|-
|| In the '''Clipper''' dialog-box, check the check-box for '''No data value'''.
||In the '''Clipper''' dialog-box, check the check-box for '''No data value'''.

Let the value be zero.

|-
|| Under the heading '''Clipping mode''',

Click on '''Extent '''radio button.
||Under the heading '''Clipping mode''',
click on '''Extent''' radio button.

|-
|| Cursor on '''QGIS''' window.

Point to cursor.

Hold left mouse and draw rectangle over Mumbai region.
||Switch to the '''QGIS''' window.

The cursor is now seen as '''plus'''(+) sign.

Hold your left mouse button and draw a rectangle covering the area of interest.

|-
|| Point to Mumbai region.
|| For this demonstration I will select Mumbai region.

|-
|| In the '''Clipper''' dialog-box, check the check-box next to '''Load into canvas when finished'''.
||In the '''Clipper''' dialog-box, check the check-box next to '''Load into canvas when finished'''.

|-
|| Click on '''OK''' button at the bottom right corner.
||Keep other default settings as such.

Click on '''OK''' button at the bottom right corner.

|-
|| Finished dialog-box opens.

Click on '''OK'''.

Click '''OK''' button in the '''Qgis.bin''' dialog-box.
||Once the process completes, close the pop-up windows by clicking on '''OK''' buttons.

|-
|| Click on '''Close''' button at the bottom right corner in the '''Clipper''' dialog-box .
|| Click on '''Close''' button  at the bottom right corner in the '''Clipper''' dialog-box.

|-
|| Point to '''Clip-DEM layer'''.
||On the canvas you will see a new layer loaded.

|-
||Uncheck check boxes for '''srtm 51 09, Hillshade, Slope layers'''.
||Disable all the layers in the '''Layers Panel''', except '''Clip-DEM''' layer.

|-
|| Cursor on the map.
|| Now we are ready to generate contour lines for this map using '''Contour''' tool.

|-
|| Click on the '''Raster''' menu, select '''Extraction''', from the sub-menu, Click on '''Contour'''.
||Click on the '''Raster '''menu.

Scroll down to '''Extraction'''.

From the sub-menu, click on '''Contour'''.

|-
|| Cursor on '''Contour''' dialog-box.

From the '''Input file''' drop-down select '''Clip-DEM''' layer. 
||'''Contour''' dialog-box opens.

From the '''Input file''' drop-down, select '''Clip-DEM''' layer. 

|-
|| Click on '''Select '''button next to '''Output file '''field.

'''Select the raster file to save the results to''' dialog box opens.
||Click on '''Select '''button for the '''Output file'''.

Dialog-box opens.

|-
|| Name the file as '''Contour.shp.'''

Click on '''Save '''button.
||In the dialog-box, name the file as '''Contour.shp'''.

Click on '''Save''' button.

|-
|| In the '''Contour''' dialog box, select '''Interval between contour lines''' as 50. 
||In the '''Contour''' dialog box, select '''Interval between contour lines''' as 50. 

This will generate contour lines for 50 meter intervals.

|-
|| Click on the check-box next to '''Attribute name'''.
||Click on the check-box next to '''Attribute name'''.

Elevation value for each contour line will be recorded as an attribute '''E L E V'''. 

|-
|| Check the box next to '''Load into canvas when finished'''.

Click on '''OK''' button.
||Check the box next to '''Load into canvas''' '''when finished'''.
Click on '''OK''' button at the bottom right corner in the contour dialog box.

|-
|| Finished dialog-box opens.

Click on '''OK'''.

Click '''OK''' button in the '''Qgis.bin''' dialog-box.
||Once the process completes, close the pop-up windows by clicking on '''OK''' buttons.

|-
|| Click on '''Close''' button.
|| Click on '''Close''' button to close the '''Contour''' dialog-box.

|-
|| Cursor on '''Contour''' layer.
||A new layer '''Contour''' is added in the '''Layers panel'''.

|-
|| Right click on '''Contour''' '''Layer'''.

Select '''Styles'''.

Rotate the triangle to change the colour.
||Let us change the colour of the contour lines.

Right click on '''Contour''' layer.

Select '''Styles'''.

Rotate the triangle to change the colour.

Choose the colour of your choice.

|-
|| Uncheck check boxes for 

'''srtm 51 09, Clip-DEM '''layer.
|| Hide the other layers by un-checking the check-boxes in the '''Layers panel'''.

|-
|| Right-click on the '''Contour''' layer, click on '''Open Attribute table'''.
||Open the '''Attribute table '''for the '''Contour''' layer.

|-
|| Point to '''ELEV''' column on the attribute table.

||In the attribute table, each line feature has an attribute named '''E L E V'''.

The value given in this column is the height in meters for that contour line.

|-
|| Click on '''ELEV''' column header.
||Click on the column header a few times to sort the values in descending order. 

|-
|| Point to 1<sup>st</sup> row.
|| The first row represents the highest elevation in our data.

|-
|| Point to last row.
||Scroll down the table, the last row represents the lowest elevation.

|-
|| Click on the first row.

Click on '''Zoom map to the selected rows''' button in the menu bar.
||Scroll up and click on the first row to select it

Click on '''Zoom map to the selected rows''' button on the tool bar.

|-
|| Point to map on '''QGIS''' canvas.
||Switch to the '''QGIS''' window.

You will see the selected contour line highlighted in yellow. 

|-
|| Point to the highlighted point.
||This is the area of the highest elevation in this '''data-set'''.

|-
|| Click on “'''Save As'''” tool on tool bar.

Type “Contour-Mumbai” 

Select “'''Desktop'''” as Location.

Click on '''Save''' button. 
||Save this project.

Click on “'''Save As'''” tool on the tool bar.

Give an appropriate name.

Save it at a convenient location.

Click on '''Save''' button. 

|-
|| '''Slide Number 7'''

'''Summary'''
|| Let us summarize,

In this tutorial we have learnt to

* Clip the area in '''DEM''' using the '''Clipper''' tool.

* Show '''contour''' lines for the '''DEM'''.

* Mark the highest elevated area on the '''contour''' map.

|-
|| '''Slide Number 8'''

'''Assignment '''

* Create '''contour '''lines for the area of your choice on the '''DEM'''.

* Find the highest elevation for the area. 


||Here is the assignment.
* Create '''contour '''lines for the area of your choice on the '''DEM'''.

* Find the highest elevation for the area. 

|-
|| '''Slide Number 9'''

'''About the Spoken Tutorial Project'''
||This video summarizes the Spoken Tutorial project.

Please download and watch it.

|-
|| '''Slide Number 10'''

'''Spoken Tutorial Workshops'''

|| The spoken tutorial project team conducts workshops and gives certificates. 

For more details please write to us.  

|-
|| '''Slide Number 11'''

'''Forum for specific question'''

|| Please post your timed queries in this forum.  

|-
|| '''Slide Number 12'''

'''Acknowledgements'''
||The Spoken Tutorial Project is funded by '''NMEICT, MHRD''' '''Government of India'''. 

This tutorial is contributed by Vaishnavi Honap from College of Engineering Pune.

Snehalatha Kaliappan and Himanshi Karwanje from IIT Bombay.

Thank you for joining. 
|-
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