Snehalathak at 06:44, 21 December 2018

2018-12-21T06:44:26Z

Nancyvarkey at 05:27, 20 December 2018

2018-12-20T05:27:27Z

Snehalathak: Created page with " {|border=1 ||'''Visual Cue''' ||'''Narration''' |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Geometric Properties of Vectors'''. |- || '''..."

2018-12-14T10:09:21Z

Created page with " {|border=1 ||'''Visual Cue''' ||'''Narration''' |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Geometric Properties of Vectors'''. |- || '''..."

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{|border=1
||'''Visual Cue'''
||'''Narration'''
|-
|| '''Slide Number 1'''

'''Title Slide'''
|| Welcome to this tutorial on '''Geometric Properties of Vectors'''.

|-
|| '''Slide Number 2'''

'''Learning Objectives'''
|| In this tutorial, we will learn to

* Show selected features from the '''attribute table''' on the map.
* Add columns to the '''attribute table'''.
* Calculate statistics for the '''attributes'''.

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

'''System Requirement'''
|| To record this tutorial, I am using,

'''Ubuntu Linux '''OS version 16.04

'''QGIS''' version 2.18

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

'''Pre-requisites'''
||To follow this tutorial you should be familiar with,

'''QGIS''' interface.

If not for relevant tutorials please visit our website.

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

'''Example map to practise'''

||To practise this tutorial,

you need to download the folder given in the '''Code files''' link located below the player.

Extract the contents of the downloaded zip file.

Locate''' IND_rails.shp '''file in the extracted folder.

|-
|| Show the map on desktop.
|| I have already downloaded the '''code file''', extracted and saved in a folder on desktop.

|-
|| Double-click on '''Code-files'''.

Right-click on '''IND_rails.shp''' file.

From the context menu select '''Open with,''' '''QGIS Desktop'''.
|| Double-click on '''Code-file''' folder on the desktop to open it.

Right-click on '''IND_rails.shp '''file.

From the context menu select, '''Open with QGIS Desktop'''.

|-
||Cursor on the map.

|| '''QGIS''' interface opens.

Click on '''OK''' button to close the '''QGIS tips''' dialog-box.

|-
|| Cursor on the map.

|| Map of India with lines representing railroads opens on canvas.

|-
|| Cursor on the map.
|| We will calculate line lengths for rail roads which are operational.

To view this information we need to open the attribute table.

|-
|| Right-click on IND_rails layer in the Layers Panel.
|| Right-click on '''IND_rails''' layer in the '''Layers Panel'''.

|-
|| From the context menu select '''Open Attribute Table '''option.
|| From the '''context menu''' select '''Open Attribute Table '''option.

|-
|| Cursor on '''attribute''' table.
|| '''Attribute''' table opens.

|-
|| Point to '''EXS_DESCRI column.'''

|| The table has an '''attribute''' called '''EXS_DESCRI'''.

We can use the value of this attribute to select features which are operational.

|-
|| Cursor on EXS_DESCRI column.
|| This column shows the status of a particular railway line.

These are categorized as '''Operational''', '''Unexamined or Unsurveyed '''and '''not Usable'''.

|-
|| Cursor on EXS_DESCRI column.
|| We need to select the lines which are operational.

|-
|| Click '''Select features using an expression''' tool in the '''attribute''' table tool bar.

(It will be seen in yellow color)
|| In the '''attribute''' table window,

Click '''Select features using an expression '''tool in the tool bar.

|-
|| Cursor on '''Select By Expression '''dialog-box.
|| A new dialog-box''' Select By Expression '''opens.

|-
|| Click on black triangle next to '''Fields and Values '''option.

|| In the '''Function Editor''' panel,click on the black triangle next to '''Fields and Values''' option.

|-
|| Double click on''' EXS_DESCRI.'''

Cursor on Expression text area.''' '''
|| From the list select '''EXS_DESCRI''' attribute.Double-click on it and add it to the '''Expression''' text area.

|-
|| Type the expression

'''<nowiki>= 'Operational'.</nowiki>'''

Click '''Select '''button.

Click '''Close '''button.
|| Complete the expression by typing

'''"EXS_DESCRI" equal to''', in '''single quotes''' '''Operational'''

|-
|| Cursor on the expression.
|| Please note, the syntax here is case sensitive.

Type the words as they appear in the '''attribute table.'''

Here “O” in '''Operational''' is Capital letter.

|-
|| Click on '''Select''' button followed by '''Close '''button at the bottom of the table.
|| At the bottom of the table, click on '''Select''' button followed by '''Close '''button.

|-
|| Point to the selected category.

Close the attribute table.
|| The '''Operational''' category are selected in the attribute table.

Close the '''attribute table'''.

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

|| On the map, you will see that all lines that fall in '''Operational''' category are selected.

These lines appear in yellow.

|-
|| Right click on IND_rails from the context menu, select '''Save Selection As.... option.'''
|| Now let’s save our selection to a new '''shapefile. '''

Right-click on '''IND_rail '''layer and select '''Save As....'''option.

|-
|| Cursor on '''Save Vector Layer as ….. dialog-box.'''
|| '''Save Vector Layer as ….. '''dialog-box opens.

|-
|| Click on '''Browse''' button.
|| Click on '''Browse''' button, next to '''File name '''field.

|-
|| In '''Save Layer As...''' dialog-box.

'''Type railway.shp in the name field.'''
|| '''Save Layer As...''' dialog-box opens.

Name the output file as '''railway.shp.'''

|-
|| Select''' Desktop.'''

Click on '''Save''' button.
|| Select a location, I will choose '''Desktop.'''

Click on '''Save''' button.

|-
||
|| Now let us select '''CRS''' for this layer.

Click on '''Select CRS '''button.

|-
|| Cursor on '''Coordinate Reference System Selector'''.
|| '''Coordinate Reference System Selector '''dialog-box opens.

|-
|| Type Indian 1975 in the '''Filter''' search box.

|| Since we are interested in calculating length, let us select an''' equidistance projection'''.

Type '''Indian 1975''' in the '''Filter''' search box.

|-
|| Select '''Indian 1975 EPSG:4240.'''
|| Under '''Coordinate Reference Systems''' of the world,

in '''Geographic Coordinate Systems''' section.

select '''Indian 1975 EPSG:4240.'''

|-
||Click on '''OK''' button.
||Click on '''OK''' button.

|-
||Cursor on '''Save vector layer as... '''dialog-box.
||In the '''Save vector layer as... '''dialog-box,

by default, '''Add saved file to map''' is already checked.

|-
|| Tick '''Save only selected features''' box.
|| Check '''Save only selected features '''check box.

|-
|| Click on '''OK''' button.
|| Click on '''OK''' button.

|-
|| Cursor on '''railway''' layer in '''Layers Panel'''.
|| Once the export process finishes, you will see a

new layer '''railway''' loaded in '''Layers Panel'''.

|-
|| Uncheck the box next to '''IND_rail''' layer.
|| In the '''Layers Panel''',

you can uncheck the box next to''' IND_rail '''layer,

to turn it off as we don’t need it any more.

|-
|| Cursor on the canvas.
|| On the canvas you will see the map of India with only operational railway lines.

|-
|| Right-click on the '''railway''' layer and select '''Open Attribute Table'''.
|| Right-click on the '''railway''' layer and select '''Open Attribute Table'''.

|-
|| Cursor on attribute table.
|| Now we will add a column with length of each feature.

|-
|| Click '''Toggle editing''' button on the tool bar.
|| Put the layer in editing mode by clicking on the '''Toggle editing''' tool on the tool bar.

|-
|| Click on '''Open field calculator''' icon on the right-hand corner of the tool bar.
|| Then click the '''Open field calculator''' button,

available on the right-hand corner of the tool bar.

|-
|| In the '''Field Calculator '''dialog-box, check '''Create a new field '''option.
|| In the '''Field Calculator '''dialog-box, check '''Create a new field check box'''.

|-
|| In the '''Output field name text box, t'''ype length-km.
|| Type '''length-km''' in the '''Output field name '''text box.

|-
|| Choose '''Decimal number (real)''' as the '''Output field type'''.
|| Choose '''Decimal number (real)''' as the '''Output field type'''.

|-
|| Increase the''' precision''' to 2.
|| Change the output '''Precision''' to 2.

|-
|| Click the triangle next to Geometry, select '''$length'''.

|| In the '''Function editor panel''',

Click the triangle next to '''Geometry '''and select''' $length'''.

|-
|| Double click on '''$length.'''
|| Double-click on '''$length''' to add it to the '''Expression''' text box.

|-
|| Type, $length / 1000

Click on '''Division Operator''' button on top of the text window.

Type 1000
|| Complete the expression as '''$length '''divided by 1000.

Click on '''Division Operator''' button on top of the text window.

Type 1000 on the keyboard.

|-
|| Click on '''OK''' button.
|| We need to divide the output length by 1000,

because '''railway''' layer '''CRS''' is in meters unit and we want the output in kilo meters.

Click on '''OK''' button.

|-
|| Click on '''Toggle editing''' tool.
|| Click on '''Toggle editing''' tool to stop editing.

|-
|| In the '''Stop editing''' dialog-box,

click on '''save''' button,
|| In the '''Stop editing''' dialog-box,

click on '''save''' button, to save the changes to the attribute table.

|-
|| Cursor on '''Attribute''' table.

Point to '''Length_km'''.
|| Back in '''attribute''' table, a new column '''Length_km '''has been added.

|-
|| Cursor on '''Length_km '''column.
|| Now we have''' '''length of each individual line in '''Railway''' layer.

We can add it all up and find the total length.

|-
|| Cursor on '''Attribute''' table.
|| Close the '''attribute table.'''

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

Select '''Analysis Tools''' option.

From the sub-menu, click on '''Basic Statistics for numeric tools''' option.
|| Click on''' Vector''' menu on the menu bar.

Select '''Analysis Tools''' option.

From the sub-menu, click on '''Basic Statistics for numeric tools'''.

|-
|| '''Basic Statistics for numeric tools '''dialog-box opens.
|| A dialog-box opens.

|-
|| Click on '''Input vector layer, '''choose '''railway.'''

Click on '''Field to calculate statistics on, '''choose''' length_km'''.
|| Select '''Input vector layer''' as '''railway'''.

Choose '''Field to calculate statistics on''' as '''length_km'''.

|-
|| Click on '''Run '''button.
|| Click on '''Run '''button at the bottom right corner of the dialog-box.

|-
|| Point to '''Sum value.'''
|| '''Results''' window opens.

Here you will see various statistics results.

The '''Sum value''' shown here is the total length of the railroads.

|-
|| Cursor on the '''Results''' window.
|| Note, The answer may vary slightly if a different projection is chosen.

|-
|| Cursor on the '''Results''' window.
|| In practice, line lengths for roads and other linear features are measured on the ground.

These values are provided as '''attributes''' to the dataset.

|-
|| Cursor on the '''Results''' window.
|| The method demonstrated above works in the absence of such attribute,

and as an approximation of actual line lengths.

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

Summary
|| Let us summarize,

In this tutorial we have learnt to,

* Show selected features from the '''attribute table''' on the map.
* Add columns to the '''attribute table'''.
* Calculate statistics for the '''attributes'''.

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

Assignment
|| Assignment

* Use the code file '''world_1.shp''', downloaded from the '''Code files''' link.<br/>

* Find the area in square-kilometers for different countries.

|-
|| Cursor on the asignment.
|| Your completed assignment should look as shown here.

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

'''About the Spoken Tutorial Project'''
||The video at the following link summarises the spoken tutorial project.
* Please download and watch it.

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

'''Spoken Tutorial Workshops'''
|| * The spoken tutorial project team conducts workshops and gives certificates on passing online tests
* For more details please write to us.

|-
|| '''Slide number 10'''

'''Forum for specific questions:'''
|| Please post your timed queries on this forum.

|-
|| '''Slide number 11'''

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

More information on this mission is available at the following link.

|-
|| '''Slide number 11'''

'''Acknowledgements'''
|| This tutorial is contributed by Prajwal.M from NIT Surathkal and Snehalatha from IIT Bombay.

Thank you for joining.

|}

← Older revision		Revision as of 06:44, 21 December 2018
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−	\|\| On the map, you will see that all lines that fall in ''Operational category''' are selected.	+	\|\| On the map, you will see that all lines that fall in '''Operational category''' are selected.

QGIS/C2/Geometric-Properties-of-Vectors/English - Revision history

Snehalathak at 06:44, 21 December 2018

Nancyvarkey at 05:27, 20 December 2018

Snehalathak: Created page with " {|border=1 ||'''Visual Cue''' ||'''Narration''' |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Geometric Properties of Vectors'''. |- || '''..."