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

Snehalathak at 07:59, 5 April 2019

2019-04-05T07:59:08Z

Snehalathak at 07:39, 5 April 2019

2019-04-05T07:39:43Z

Snehalathak at 07:28, 5 April 2019

2019-04-05T07:28:55Z

Snehalathak at 07:12, 4 April 2019

2019-04-04T07:12:04Z

Snehalathak at 06:49, 4 April 2019

2019-04-04T06:49:33Z

Nancyvarkey at 11:50, 2 April 2019

2019-04-02T11:50:33Z

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Snehalathak at 12:24, 29 March 2019

2019-03-29T12:24:24Z

Snehalathak: Created page with " {|border=1 ||'''Visual Cue''' ||'''Narration''' |- |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''. |-..."

2019-03-29T11:26:44Z

Created page with " {|border=1 ||'''Visual Cue''' ||'''Narration''' |- |- || '''Slide Number 1''' '''Title Slide''' || Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''. |-..."

New page

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

'''Title Slide'''
|| Welcome to this tutorial on '''Raster Data Styling''' in '''QGIS'''.

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

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

*to style a continuous '''raster'''.
*to write an expression in '''Raster Calculator'''.
*About '''raster''' properties.

|-
|| '''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'''

'''https://spoken-tutorial.org/'''
|| To follow this tutorial you should be familiar with,

'''QGIS''' interface.

For the prerequisite tutorials please visit our website.

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

'''Example for Demonstration'''
|| Download the folder given in the '''Code files''' link, located below the player.

Extract the contents of the downloaded zip file and save it in a folder.

|-
|| Point to '''Code-file''' folder on desktop.

Double-click on '''Code-file''' folder.
|| Here is my '''Code files''' folder.

Double click to open the folder.

|-
|| Point to''' glds00ag60.asc '''and''' glds90ag60.asc '''files.

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

There are two files in '''ASCII''' format, with .asc file extension.

Let us open these files in '''QGIS'''.

Close the '''Code files''' folder.

|-
|| Open '''QGIS''' interface.

Click on '''Layer''' menu, from the drop-down menu select '''Add Raster Layer'''.
|| Here I have opened '''QGIS''' interface.

Click on '''Layer''' menu.

From the drop-down select '''Add Layer'''.

From the sub-menu select '''Add Raster Layer'''.

|-
|| Point to''' Raster Data Source '''dialog-box.

Press and hold the ctrl key, click on both the files.

pop-1990 and pop-2000.
|| A dialog-box opens, I will navigate to the '''Code file '''folder on the '''desktop'''.

Select the two files with .asc file extension.

Press and hold the ctrl key, click on both the files.

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

|-
|| Cursor on''' Coordinate Reference System Selector'''.

Select '''WGS 84 EPSG:4326 '''from the list.

Click on '''OK''' button.
|| '''Coordinate Reference System Selector''' opens.

In some settings CRS will be selected automatically, in such a situation this window may not open.

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

Here I will select '''WGS 84 EPSG 4326 '''from the list.

Click on '''OK''' button.

|-
|| Cursor on''' Coordinate Reference System Selector'''.

Select '''WGS 84 EPSG:4326 '''from the list.

Click on '''OK''' button.
|| Since we are adding two layers at the same time,

'''Coordinate Reference System Selector''' opens once more here.

Again select '''WGS 84 EPSG 4326 '''

Click on '''OK''' button.

|-
|| Cursor on world map.
|| On the canvas you will see a world map rendered in '''grayscale.'''

Lighter '''pixels''' indicate higher population and darker '''pixels''' indicate lower population.

|-
|| Cursor on''' Layers panel'''.
|| In the '''Layers Panel''', you will see both the raster layers loaded.

|-
|| Cursor on map.
(Zoom-in the map)
|| Each pixel in the raster has a value of population density for that grid.

|-
|| Click on '''Identify Features''' tool on the tool bar. (blue square icon with small i)
|| To see the value of the pixel,

click on '''Identify Features''' tool on the top-right corner of the tool bar.

|-
|| Click on a pixel on map.

Point to the value.
|| Use the mouse wheel to zoom in the map.

Click anywhere on the raster map.

The pixel value will be displayed in the '''Identify Results''' panel.

|-
|| Click on darker pixel.

Click on lighter pixel.
|| Observe that lighter pixel has higher value the darker pixel has lower value.

Close the '''Identify Results''' panel.

|-
|| Cursor on canvas.
|| Zoom out the map.
Click on '''Pan Map''' tool and adjust the map on the canvas.

|-
||
|| Population density pattern can be better visualized with an appropriate type of styling.

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

Select''' Properties '''option.
|| Right-click on the 1st layer in the '''Layers''' Panel.

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

|-
|| Cursor on '''Layer Properties '''dialog-box.
|| '''Layer Properties''' dialog-box opens.

|-
|| '''Style>>Render type>> Singleband pseudocolor'''
|| In the dialog-box box select '''Style''' tab.
Under '''Band Rendering''' section, change the '''Render type''' to '''Singleband pseudocolor'''.

|-
|| Under '''Load min/max values, '''click on '''Colors '''text box drop-down.

choose '''Plasma'''.
|| Let the Intropolation be '''Linear'''.

In the '''Color''' drop-down, select '''Spectral'''.

|-
|| Click on''' Classify button. '''

(Maximise the properties dialog-box).

Cursor on '''Value''' column.

|| Scroll down.

Select number of '''Classes''' as 5.

'''Mode''' as '''Continuous'''.

Click on '''Classify '''button.

|-
|| Cursor on the middle panel.
|| You will see 5 new color values created.

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

|-
|| Cursor on '''QGIS''' Canvas.

|| Back in the '''QGIS''' Canvas,

you will see the raster map displayed in 5 classes of spectral color rendering.

|-
|| Properties>>Style>>Render type>> Singleband pseudocolor>> Classify
|| Follow the same steps as shown for 1st layer and change the raster style for 2nd layer.

|-
|| Cursor on the canvas.
|| For our analysis,

we would like to find areas with largest population change between years 1990 and 2000.

|-
|| Cursor on panel.
|| For this,

we need to find the difference between each grid’s pixel values in both the layers.

For these calculations we will use '''Raster Calculator tool'''.

|-
|| Click on '''Raster menu '''from the menu bar.

From the drop-down, click on '''Raster calculator'''.
|| Click on '''Raster''' menu from the menu bar.

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

|-
|| '''Raster Calculator '''dialog-box opens.
|| '''Raster Calculator''' dialog-box opens.

|-
|| Cursor on '''Raster bands''' section.

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

Since each of our rasters have only 1 band, you will see only 1 entry per raster.

|-
|| Cursor on '''Raster bands''' section.
|| The raster calculator can apply mathematical operations on the raster pixels.

|-
|| Cursor on '''Raster bands''' section.
|| In this case we want to enter a simple formula to subtract,

the population density for the year 1990 from population density for the year 2000.

|-
|| Double-click on the raster layer for the year 2000 (pop-2000@1).
|| Under '''Raster bands''' section, select the layer by double-clicking on the raster layer for the year 2000.

|-
|| Point to '''Raster calculator expression''' section.
|| The expression is now added to the '''Raster calculator expression''' section.

|-
|| From the '''Operators''' section click on subtraction operator.

From the '''Raster bands''' section double-click on raster layer for the year 1990 (pop-1990@1).
|| From the '''Operators''' section click on subtraction operator button.

Again from the '''Raster bands''' section double-click on raster layer for the year 1990.

|-
|| Cursor on formula.

pop-2000@1 - pop-1990@1
|| The formula for the calculation is now displayed in the '''Raster calculator expression''' section.

|-
|| '''Result Layer''' section, in the '''Output layer''' box,

In the '''output layer''' field, type, '''pop-density-change.tif'''
|| Under '''Result Layer''' section, you will see

'''Output layer''' box.

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

|-
|| '''Output format''' as '''Geo TIFF.'''
|| In the''' Output format '''drop-down''' '''select '''Geo TIFF. '''

|-
|| Cursor on '''Output CRS''' option.
|| '''Output CRS''' option is automatically selected, leave as such.

|-
|| Check the box next to '''Add result to project'''.
|| Check the box next to '''Add result to project'''.

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

|-
|| Cursor on '''Layers Panel.'''
|| You will see the new layer load in '''Layers Panel'''.

|-
|| In the layers panel, uncheck the check boxes for pop-2000 and pop-1990 layers.
|| To view the map for the 3rd layer,

in the layers panel, uncheck the check boxes for pop-2000 and pop-1990 layers.

|-
|| Cursor on canvas.
|| We can create a much more informative map by changing the style of this layer.

|-
|| Right-click on the '''pop-density-change''' layer.

From the '''context''' menu select '''Properties''' option.
|| Right-click on the '''pop-change''' layer.

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

|-
|| Cursor on '''Layer Properties''' dialog-box.
|| '''Layer Properties''' dialog-box opens.

|-
|| Cursor on the canvas.
|| We want to style the layer such that, pixel values in certain ranges get the same color.

|-
|| Click on Metadata tab

Scroll down and point towards minimum and maximum values.

STATISTICS_MAXIMUM=5775.919921875

STATISTICS_MINIMUM

<nowiki>=-1840.7290039062</nowiki>

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

Note the '''maximum''' and '''minimum.'''

Maximum value is close to 6000.

Minimum value is just above -2000.

|-
|| Click on '''Style''' tab.

'''Band Rendering >>Render type s'''elect '''Singleband pseudocolor.'''
|| Now go to the '''Style''' tab.

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

|-
|| '''interpolation>> Discrete'''
|| Set the '''interpolation''' to '''Discrete'''.

|-
|| Click the '''Add Values Manually''' (green plus symbol button located next to Classify button) button 4 times.

Cursor on the values.
|| Scroll down.

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

This is a green plus symbol button located next to '''Classify''' button.

Click the '''Add Values Manually''' button 4 times to create 4 unique classes.

These values show-up in the middle panel.

|-
|| Cursor on the values.
|| Here we have to change the values in each row.

Population values lower than the value entered will be given the color of that entry.

|-
|| Double click on value in the Value column.
|| Double-click on the first entry in the Values column to change the value.

|-
|| Type -2000.

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

Type -2000 in the first entry.

|-
|| Double-click on the color-box and change the color. Red color
|| Double-click on the color-box and change the color.

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

Type, '''No Data values'''.
|| Double-click on the '''Label '''column in the first row.

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

|-
|| Point to the table.
|| Similarly fill in all the values and labels as shown here.

|-
|| Point to the table.

Light Green
|| In the 2nd row, -10 to denote negative change.

|-
|| Point to the table.

Pink
|| In the 3rd row, 10 to denote neutral.

|-
|| Point to the table.

Blue
|| Finally 6000 to denote Positive change.

Because our maximum value from the meta data analysis is close to 6000.

|-
|| Click on '''OK''' button.
|| At the bottom-right corner of the window,

click on '''Apply '''button and then '''OK''' button.

|-
|| Point to the map on the canvas.
|| Now on the canvas you will see a much more powerful visualization of the population data.

Here you can see clearly areas which has seen positive and negative population density changes.

|-
||
|| Areas colored in blue denote the positive population.

Areas in green show negative change.

Areas in pink have not see too much population change.

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

Summary
|| Let's summarize,

In this tutorial we have learnt,

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

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

Assignment
|| As an assignment

*Using the population data given in the '''Code files''' link,

*Create a new raster file which shows only negative population change.

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

|-
||
|| Your completed assignment should look as shown here.

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

'''Acknowledgement'''
|| The video at the following link summarises the spoken tutorial project. Please download and watch it.

|-
|| '''Slide Number 13'''
|| The spoken tutorial project team conducts workshops and gives certificates on passing online tests

For more details please write to us.

|-
||
|| Please post your timed queries on this forum.

|-
|| '''Slide number 14'''
|| 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 14'''
|| This tutorial is contributed by Prajwal.M from NIT Surathkal and Snehalatha from IIT Bombay.

Thank you for watching.

|}

@@ Line 501: / Line 501: @@
 |-
-||
+|| Point to the map on the canvas.
 || Areas colored in blue denote the positive population change.
@@ Line 530: / Line 530: @@
 |-
-||
+|| Show images of assignment.
 || Your completed assignment should look as shown here.

@@ Line 326: / Line 326: @@
-In the '''output layer field''', type, '''pop-density-change.tif'''
+In the '''output layer field''', type, '''pop-density-change.tif'''.
 || Under '''Result Layer''' section, you will see '''Output layer''' box.
-In the box, type the name of your '''output layer''' as '''pop-change.tif'''
+In the box, type the name of your '''output layer''' as '''pop-change.tif'''.
 |-

@@ Line 185: / Line 185: @@
 Click on lighter pixel.
-|| Observe that the lighter '''pixel''' has higher value the darker '''pixel''' has lower value.
+|| Observe that the lighter '''pixel''' has higher value and the darker '''pixel''' has lower value.
@@ Line 230: / Line 230: @@
 |-
 ||
 (Maximise the properties dialog-box).
@@ Line 242: / Line 236: @@
 || Scroll down.
 '''Mode''' as '''Continuous'''.
@@ Line 306: / Line 296: @@
 || In this case we want to enter a simple formula
 *to subtract the population density for the year 1990
-*from population density for the year 2000.
+*from the population density for the year 2000.
 |-
@@ Line 364: / Line 354: @@
 |-
 || In the '''Layers Panel''', uncheck the check boxes for pop-2000 and pop-1990 layers.
-|| To view the map for the 3rd layer, in the '''Layers Panel''', uncheck the check boxes for pop-2000 and pop-1990 '''layers'''.
+|| To view the map for the 3rd layer,
 |-
@@ Line 402: / Line 393: @@
-Note the '''maximum''' and '''minimum.'''
+Note the '''maximum''' and '''minimum '''values.
@@ Line 513: / Line 504: @@
 |-
 ||
-|| Areas colored in blue denote the positive population.
+|| Areas colored in blue denote the positive population change.
 Areas in green show negative change.
@@ Line 522: / Line 513: @@
 || '''Slide Number 6 '''
 Summary
-|| Let's summarize,
+|| Let us summarize,
 In this tutorial we have learnt,

@@ Line 107: / Line 107: @@
-Press and hold the '''Ctrl''' key, and click on both the files.
+Press and hold the '''Ctrl''' key, click on both the files.
 |-
@@ Line 185: / Line 185: @@
 Click on lighter pixel.
-|| Observe that lighter '''pixel''' has higher value the darker '''pixel''' has lower value.
+|| Observe that the lighter '''pixel''' has higher value the darker '''pixel''' has lower value.

@@ Line 215: / Line 215: @@
 |-
 || '''Style>>Render type>> Singleband pseudocolor'''
-|| In the dialog-box box select '''Style''' tab.
+|| In the dialog-box select '''Style''' tab.
@@ Line 237: / Line 237: @@
 || Scroll down.
-'''Mode''' as '''Continuous'''.
+Select '''Mode''' as '''Continuous'''.
@@ Line 338: / Line 338: @@
 |-
 || Cursor on '''Output CRS''' option.
-|| '''Output CRS''' option is automatically selected.  Leave as such.
+|| '''Output CRS''' option is automatically selected.  Leave it as such.
 |-
@@ Line 383: / Line 383: @@
 Scroll down and point towards minimum and maximum values.
 STATISTICS_MAXIMUM=5775.919921875
-STATISTICS_MINIMUM
+STATISTICS_MINIMUM=-1840.7290039062
 || Click on '''Metadata''' tab, scroll down to '''Properties''' section.
@@ Line 423: / Line 421: @@
-Locate '''Add Values Manually '''button.
+Locate '''Add Values Manually''' button.
@@ Line 528: / Line 526: @@
 *Using the population data given in the '''Code files''' link,
-*:Create a new raster file which shows only negative population change.
+*Create a new raster file which shows only negative population change.
 *Hint: Use '''Raster Calculator''', write an expression to select population change less than 0.

@@ Line 535: / Line 535: @@
 |-
-|| '''Slide Number 10'''
+|| '''Slide Number 6 '''
-−
 Summary
 || Let's summarize,
@@ Line 549: / Line 548: @@
 |-
-|| '''Slide Number 11'''
+|| '''Slide Number 7'''
 Assignment
@@ Line 567: / Line 566: @@
 |-
-|| '''Slide Number 12'''
+|| '''Slide Number 8'''
-'''Acknowledgement'''
+'''About Spoken Tutorial Project'''
 || The video at the following link summarises the spoken tutorial project. Please download and watch it.
 |-
-|| '''Slide Number 13'''
+|| '''Slide Number 9'''
 || The spoken tutorial project team conducts workshops and gives certificates on passing online tests
@@ Line 580: / Line 580: @@
 |-
-||
+|| '''Slide Number 10'''
 || Please post your timed queries on this forum.
 |-
-|| '''Slide number 14'''
+|| '''Slide number 11'''
 || The Spoken Tutorial Project is funded by '''NMEICT, MHRD''' Government of India.
@@ Line 590: / Line 593: @@
 |-
-|| '''Slide number 14'''
+|| '''Slide number 11'''
 || This tutorial is contributed by Prajwal.M from NIT Surathkal and Snehalatha from IIT Bombay.