QGIS/C2/Geometric-Properties-of-Vectors/English-timed

Time	Narration
00:01	Welcome to this tutorial on Geometric Properties of Vectors.
00:06	In this tutorial, we will learn to Show selected features from the attribute table on the map.
00:14	Add columns to the attribute table.
00:18	Calculate statistics for the attributes.
00:22	To record this tutorial, I am using, Ubuntu Linux OS version 16.04, QGIS version 2.18
00:34	To follow this tutorial you should be familiar with QGIS interface.
00:41	If not for relevant tutorials please visit our website.
00:46	To practise this tutorial, you need to download the folder given in the Code files link located below the player.
00:56	Extract the contents of the downloaded zip file.
01:00	Locate IND_rails.shp file in the extracted folder.
01:08	I have already downloaded the code file, extracted and saved in a folder on the Desktop.
01:15	Double-click on Code-file folder on the Desktop to open it.
01:21	Right-click on IND_rails.shp file.
01:27	From the context menu, select Open with QGIS Desktop.
01:35	QGIS interface opens.
01:38	Click on OK button to close the QGIS tips dialog-box.
01:44	Map of India with lines representing railroads opens on canvas.
01:51	We will calculate line lengths for rail roads which are operational.
01:57	To view this information we need to open the attribute table.
02:02	Right-click on IND_rails layer in the Layers Panel.
02:09	From the context menu select Open Attribute Table option.
02:14	Attribute table opens.
02:17	The table has an attribute called EXS_DESCRI.
02:25	We can use the value of this attribute to select features which are operational.
02:31	This column shows the status of a particular railway line.
02:36	These are categorized as Operational, Unexamined or Unsurveyed and not Usable.
02:48	We need to select the lines which are operational.
02:52	In the attribute table window, Click Select features using an expression tool in the tool bar.
03:00	A new dialog-box Select By Expression opens.
03:05	In the Function Editor panel, click on the black triangle next to Fields and Values option.
03:13	From the list select EXS_DESCRI attribute.
03:21	Double-click on it and add it to the Expression text area.
03:26	Complete the expression by typing "EXS_DESCRI" equal to, in single quotes Operational
03:37	Please note, the syntax here is case-sensitive.
03:42	Type the words as they appear in the attribute table.
03:47	Here “O” in Operational is capital letter.
03:52	At the bottom of the table, click on Select button followed by Close button.
03:59	The Operational category are selected in the attribute table.
04:04	Close the attribute table.
04:07	On the map, you will see that all lines that fall in Operational category are selected.
04:14	These lines appear in yellow.
04:17	Now let’s save our selection to a new shapefile.
04:22	Right-click on IND_rail layer and select Save As....option.
04:31	Save Vector Layer as ….. dialog-box opens.
04:35	Click on Browse button, next to File name field.
04:40	Save Layer As... dialog-box opens.
04:44	Name the output file as railway.shp.
04:49	Select a location, I will choose Desktop. Click on Save button.
04:57	Now let us select CRS for this layer. Click on Select CRS button.
05:04	Coordinate Reference System Selector dialog-box opens.
05:09	Since we are interested in calculating length, let us select an equidistance projection.
05:16	Type Indian 1975 in the Filter search box.
05:22	Under Coordinate Reference Systems of the world, in Geographic Coordinate Systems section select Indian 1975 EPSG:4240.
05:36	Click on OK button.
05:39	In the Save vector layer as... dialog-box, by default, Add saved file to map is already checked.
05:48	Check Save only selected features check box.
05:53	Click on OK button.
05:56	Once the export process finishes, you will see a new layer railway loaded in Layers Panel.
06:04	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.
06:15	On the canvas you will see the map of India with only operational railway lines.
06:22	Right-click on the railway layer and select Open Attribute Table.
06:29	Now we will add a column with length of each feature.
06:34	Put the layer in editing mode by clicking on the Toggle editing tool on the tool bar.
06:41	Then click the Open field calculator button, available on the right-hand corner of the tool bar.
06:49	In the Field Calculator dialog-box, check Create a new field check box.
06:55	Type length-km in the Output field name text box.
07:02	Choose Decimal number (real) as the Output field type.
07:07	Change the output Precision to 2.
07:10	In the Function editor panel, Click the triangle next to Geometry and select $length.
07:20	Double-click on $length to add it to the Expression text box.
07:26	Complete the expression as $length divided by 1000.
07:32	Click on Division Operator button on top of the text window.
07:37	Type 1000 on the keyboard.
07:40	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.
07:52	Click on OK button.
07:55	Click on Toggle editing tool to stop editing.
08:00	In the Stop editing dialog-box, click on Save button, to save the changes to the attribute table.
08:07	Back in attribute table, a new column Length_km has been added.
08:15	Now we have length of each individual line in Railway layer.
08:20	We can add it all up and find the total length.
08:25	Close the attribute table.
08:28	Click on Vector menu on the menu bar. Select Analysis Tools option.
08:36	From the sub-menu, click on Basic Statistics for numeric tools.
08:42	A dialog-box opens.
08:45	Select Input vector layer as railway.
08:50	Choose Field to calculate statistics on as length_km.
08:57	Click on Run button at the bottom right corner of the dialog-box.
09:03	Results window opens.
09:06	Here you will see various statistics results.
09:11	The Sum value shown here is the total length of the railroads.
09:16	Note, the answer may vary slightly if a different projection is chosen.
09:23	In practice, line lengths for roads and other linear features are measured on the ground.
09:30	These values are provided as attributes to the dataset.
09:35	The method demonstrated above works in the absence of such attribute And as an approximation of actual line lengths.
09:46	Let us summarize, In this tutorial we have learnt to,
09:51	Show selected features from the attribute table on the map. Add columns to the attribute table and Calculate statistics for the attributes.
10:04	As an Assignment Use the code file world_1.shp, downloaded from the Code files link.
10:14	Find the area in square-kilometers for different countries.
10:20	Your completed assignment should look as shown here.
10:26	The video at the following link summarises the spoken tutorial project. Please download and watch it.
10:34	The spoken tutorial project team conducts workshops and gives certificates on passing online tests
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10:49	The Spoken Tutorial Project is funded by NMEICT, MHRD Government of India. More information on this mission is available at the following link.
11:01	This tutorial is contributed by Prajwal.M from NIT Surathkal and Snehalatha from IIT Bombay. Thank you for joining.

Contributors and Content Editors

PoojaMoolya