PoojaMoolya: Created page with " {|border=1 ||'''Time''' ||'''Narration''' |- || 00:01 || Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''. |- || 00:07 || In this tutorial, we will learn..."

2020-09-15T05:43:53Z

Created page with " {|border=1 ||'''Time''' ||'''Narration''' |- || 00:01 || Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''. |- || 00:07 || In this tutorial, we will learn..."

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{|border=1
||'''Time'''
||'''Narration'''

|-
|| 00:01
|| Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''.

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|| 00:07
|| In this tutorial, we will learn, to style a continuous '''raster'''.

|-
|| 00:13
||To write an expression in '''Raster Calculator'''.

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|| 00:17
||About '''raster''' properties.

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|| 00:20
|| To record this tutorial, I am using,

'''Ubuntu Linux OS''' version 16.04

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|| 00:28
||'''QGIS''' version 2.18

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|| 00:32
|| To follow this tutorial you should be familiar with '''QGIS interface'''.

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|| 00:38
||For the prerequisite tutorials please visit our website.

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|| 00:43
|| Download the folder given in the '''Code files''' link, located below the player.

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|| 00:49
||Extract the contents of the downloaded zip file and save it in a folder.

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|| 00:56
|| Here is my '''Code files''' folder.

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|| 00:59
||Double-click to open the folder.

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||01:02
|| In this folder you will find '''Population Density grid files''' for the entire world, for the year 2000 and 1990.

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||01:12
||There are two files in '''ASCII''' format, with '''.asc file extension'''.

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||01:20
||Let us open these files in '''QGIS'''.

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||01:24
||Close the '''Code files''' folder.

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|| 01:27
|| Here I have opened '''QGIS''' interface.

Click on '''Layer''' menu.

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||01:34
||From the drop-down select '''Add Layer'''.

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||01:38
||From the sub-menu, select '''Add Raster Layer'''.

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|| 01:43
|| A dialog-box opens. I will navigate to the '''Code file '''folder on the '''Desktop'''.

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|| 01:52
||Select the two files with '''.asc file extension'''.

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||01:58
||Press and hold the '''Ctrl''' key, click on both the files.

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|| 02:04
|| Click on '''Open''' button.

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|| 02:07
|| '''Coordinate Reference System Selector''' opens.

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||02:11
||In some settings, '''CRS''' will be selected automatically.

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||02:17
||In such a situation this window may not open.

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||02:21
||If '''Coordinate Reference System Selector''' does not open, ignore this step and proceed with the next step.

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||02:30
||Here I will select '''WGS 84 EPSG 4326 '''from the list.

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|| 02:39
||Click on '''OK''' button.

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|| 02:42
|| Since we are adding two layers at the same time, '''Coordinate Reference System Selector''' opens once more here.

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||02:51
||Again select '''WGS 84 EPSG 4326'''.

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|| 02:58
||Click on '''OK''' button.

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|| 03:01
|| On the canvas you will see a world map rendered in '''grayscale.'''

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|| 03:07
|| Lighter '''pixels''' indicate higher population and darker '''pixels''' indicate lower population.

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|| 03:15
|| In the '''Layers Panel''', you will see both the '''raster layers''' loaded.

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|| 03:21
|| Each '''pixel''' in the '''raster''' has a value of population density for that grid.

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||03:27
|| To see the value of the '''pixel''', click on '''Identify Features''' tool on the top-right corner of the toolbar.

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|| 03:35
|| Use the mouse wheel to zoom in the map.

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|| 03:38
|| Click anywhere on the '''raster''' map.

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|| 03:41
|| The pixel value will be displayed in the '''Identify Results''' panel.

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|| 03:48
|| Observe that the lighter '''pixel''' has higher value and the darker '''pixel''' has lower value.

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|| 03:57
|| Close the '''Identify Results''' panel.

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|| 04:00
|| Zoom out the map. Click on '''Pan Map''' tool and adjust the map on the canvas.

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|| 04:09
|| Population density pattern can be better visualized with an appropriate type of styling.

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|| 04:16
|| Right-click on the 1st layer in the '''Layers Panel'''.

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|| 04:21
||From the context menu select '''Properties '''option.

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|| 04:26
|| '''Layer Properties''' dialog-box opens.

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|| 04:30
|| In the dialog-box select '''Style''' tab.

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|| 04:35
||Under '''Band Rendering''' section, change the '''Render type''' to '''Singleband pseudocolor'''.

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|| 04:42
|| Let the '''Interpolation''' be '''Linear'''.

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|| 04:46
||In the '''Color''' drop-down, select '''Spectral'''.

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|| 04:51
|| Scroll down.

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|| 04:54
||Select '''Mode''' as '''Continuous'''.

Click on '''Classify '''button.

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|| 05:00
|| You will see 5 new color values created.

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|| 05:05
|| Click on '''Apply''' button and '''OK''' button at the bottom right corner of the dialog-box.

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|| 05:14
|| Back in the '''QGIS''' Canvas, you will see the '''raster''' map displayed in 5 classes of spectral color rendering.

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|| 05:24
|| Follow the same steps as shown for 1st '''layer''' and change the '''raster style''' for 2nd '''layer'''.

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|| 05:45
|| For our analysis, we would like to find areas with largest population change between years 1990 and 2000.

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|| 05:54
|| For this, we need to find the difference between each grid’s '''pixel''' values in both the '''layers'''.

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|| 06:02
||For these calculations, we will use '''Raster Calculator tool'''.

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|| 06:07
|| Click on '''Raster''' menu from the menu bar.

From the drop-down, click on '''Raster calculator'''.

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|| 06:16
|| '''Raster Calculator''' dialog-box opens.

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|| 06:20
|| In the '''Raster bands''' section, the names of the bands are displayed.

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|| 06:26
||Since each of our '''rasters''' have only 1 band, you will see only 1 entry per '''raster'''.

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|| 06:33
|| The '''raster calculator''' can apply mathematical operations on the '''raster pixels'''.

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|| 06:40
|| In this case we want to enter a simple formula to subtract the population density for the year 1990
from the population density for the year 2000.

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|| 06:52
|| Under '''Raster bands''' section, select the '''layer''' by double-clicking on the '''raster layer''' for the year 2000.

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||07:00
|| The expression is now added to the '''Raster calculator expression''' section.

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|| 07:06
|| From the '''Operators''' section, click on subtraction operator button.

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|| 07:12
||Again from the '''Raster bands''' section, double-click on '''raster layer''' for the year 1990.

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|| 07:20
|| The formula for the calculation is now displayed in the '''Raster calculator expression''' section.

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|| 07:27
|| Under '''Result Layer''' section, you will see '''Output layer''' box.

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|| 07:33
||In the box, type the name of your '''output layer''' as '''pop-change.tif'''.

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||07:41
|| In the''' Output format '''drop-down, select '''Geo TIFF. '''

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|| 07:47
|| '''Output CRS''' option is automatically selected. Leave it as such.

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|| 07:54
|| Check the box next to '''Add result to project'''.

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|| 08:00
|| Click on '''OK''' button at the bottom of the dialog-box.

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|| 08:04
|| You will see the new '''layer''' load in '''Layers Panel'''.

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|| 08:08
|| To view the map for the 3rd layer, in the '''Layers Panel''' uncheck the check boxes for pop-2000 and pop-1990 '''layers'''.

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|| 08:21
|| We can create a much more informative map by changing the style of this '''layer'''.

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|| 08:27
|| Right-click on the '''pop-change layer'''.

From the context menu, select '''Properties''' option.

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|| 08:36
|| '''Layer Properties''' dialog-box opens.

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|| 08:40
|| We want to style the '''layer''' such that, '''pixel''' values in certain ranges get the same color.

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|| 08:47
|| Click on '''Metadata''' tab, scroll down to '''Properties''' section.

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|| 08:55
||Note the '''maximum''' and '''minimum '''values.

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|| 08:59
||Maximum value is close to 6000.

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|| 09:02
||Minimum value is just above -2000.

|-
|| 09:06
|| Go to the '''Style''' tab.

Under '''Band Rendering, '''select '''Singleband pseudocolor''' as the '''Render type'''.

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|| 09:14
|| Set the '''Interpolation''' to '''Discrete'''.

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||09:19
|| Scroll down.

Locate '''Add Values Manually''' button.

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|| 09:25
||This is a green plus symbol button located next to '''Classify''' button.

|-
|| 09:31
||Click the '''Add Values Manually''' button 4 times to create 4 unique '''classes'''.

|-
|| 09:39
||These values show-up in the middle panel.

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|| 09:43
|| Here we have to change the values in each row.

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|| 09:47
||Population values lower than the value entered, will be given the color of that entry.

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|| 09:54
|| Double-click on the first entry in the '''Values''' column to change the value.

|-
|| 10:00
|| We have observed, the minimum value in our '''metadata''' analysis is just above -2000.

Type -2000 in the first entry.

|-
|| 10:12
|| Double-click on the color-box and change the color.

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|| 10:20
|| Double-click on the '''Label '''column in the first row.

Type, '''No Data values'''.

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|| 10:28
|| Similarly fill in all the values and labels as shown here.

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||10:33
|| In the 2nd row, -10 to denote '''Negative''' change.

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|| 10:46
|| In the 3rd row, 10 to denote '''Neutral'''.

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|| 10:59
|| Finally 6000 to denote '''Positive''' change.

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|| 11:03
||Because our maximum value from the meta data analysis is close to 6000.

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|| 11:23
|| At the bottom-right corner of the window, click on '''Apply '''button and then '''OK''' button.

|-
|| 11:30
|| Now on the canvas you will see a much more powerful visualization of the population data.

|-
|| 11:37
||Here you can see clearly areas which has seen positive and negative population density changes.

|-
|| 11:46
|| Areas colored in blue denote the positive population change.

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|| 11:52
||Areas in green show negative change.

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|| 11:56
||Areas in pink have not see too much population change.

|-
|| 12:02
|| Let us summarize,

|-
|| 12:04
||In this tutorial we have learnt,

to style a continuous '''raster''', to write an expression in '''raster calculator''', About '''raster''' properties.

|-
||12:17
|| As an assignment

Using the population data given in the '''Code files''' link, Create a new raster file which shows only negative population change.

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|| 12:28
||Hint: Use '''Raster Calculator''', write an expression to select population change less than 0.

|-
|| 12:36
|| Your completed assignment should look as shown here.

|-
|| 12:41
|| The video at the following link summarises the spoken tutorial project. Please download and watch it.

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|| 12:49
|| The spoken tutorial project team conducts workshops and gives certificates on passing online tests

For more details please write to us.

|-
|| 13:00
|| Please post your timed queries on this forum.

|-
||13:04
|| The Spoken Tutorial Project is funded by '''NMEICT, MHRD''' Government of India.

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

|-
|| 13:16
|| This tutorial is contributed by Prajwal.M from NIT Surathkal and Snehalatha from IIT Bombay.

Thank you for watching.

|}

QGIS/C2/Raster-Data-Styling/English-timed - Revision history

PoojaMoolya: Created page with " {|border=1 ||'''Time''' ||'''Narration''' |- || 00:01 || Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''. |- || 00:07 || In this tutorial, we will learn..."