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Mon Jul 6 15:00:08 2015

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QGIS Planet

Create great looking topographic maps in QGIS

Wicklow-Topo-original

In this tutorial I will show you how to create a Hillshaded topographic map in QGIS. We will be using Shuttle Radar Topography Mission (SRTM) data, a near global Digital Elevation Model (DEM) collected in February 2000 aboard NASA’s Space Shuttle Endeavour (mission STS-99). The mission used a X-Band mapping radar to measure the Earth’s topography, built in collaboration with the U.S. Jet Propulsion Laboratory, the U.S. National Imagery and Mapping Agency (now the National Geospatial-Intelligence Agency), and the German and Italian space agencies.

The raw radar data has been continuously processed and improved since it was first collected. Countless artefacts have been painstakingly removed and areas of missing data have been filled using alternate data sources. The version we will be using is the 1 Arc-Second Global SRTM dataset, an enhanced 30 meter resolution DEM that was released last year. It is a substantial improvement over the 3 Arc-Second / 90 meter SRTM data previously available for Ireland. SRTM elevation data can be downloaded from the United States Geological Survey’s EarthExplorer website.

When first loaded into QGIS (via Add Raster Layer), the DEM is displayed as a rather uninformative black and white image.

Wicklow-Topo-blackwhite

It is therefore necessary to apply a suitable colour ramp that accentuates topography. While it is possible to create your own colour ramp, or use one of the colour ramps provided by QGIS, superior colour ramps can be downloaded using Etienne Tourigny’s Color Ramp Manager (Plugins – Manage and Install Plugins). After the plugin is added to QGIS, go to the Plugins menu again and choose the Colour Ramp Manager.

In the window that pops up, choose the full opt-city package and click check for update. The plugin will then download the cpt-city library, a collection of over a hundred cartographic gradients (version 2.15). After the package downloads, quit the dialogue.

Back in QGIS, right click the DEM layer to bring up the Layer Properties dialogue. In the Style tab, change the render type from single band grey to single band pseudocolor. Then click new color ramp and new color ramp again, choose the cpt-city color ramp to bring up the cpt-city dialogue. Click topography and choose the sd-a colour ramp. While this is an excellent colour ramp, I find its colours are a bit too strong for my liking.

Still in the Layer Properties dialogue, change the min and max values to match your DEM’s lowest and highest elevations values and click classify, this applies the new colour ramp. Next, change the brightness to 30 and lower the contrast and saturation to -20. Click OK to apply the new style and quit the Layer Properties dialogue.

Wicklow-Topo-noShade

Next we need to create a Hillshade layer from the DEM, a 3D like visual representation of topographic relief. This is achieved via the menu Raster – Analysis – DEM (Terrain models). There is one small catch, the hillshading algorithm assumes the DEM’s horizontal units are in meters (they are decimal degrees). We need to enter a scale correction factor of 111120 (in the Scale ratio vert. units to horiz. box). Once that is all done, select an output path to save the generated hillshade and click OK. Generating a hillshade may take up to a minute depending on the size of your DEM.

Wicklow-Topo-hillshade

After the hillshade is created, open its Layer properties dialogue. Change the min and max values to 125 and 255, increase its brightness to 45 and contrast to 20. Finally, switch the blending mode from normal to multiply. This allows the DEM beneath the hillshade to show though. Click OK to apply the new style.

If you followed these steps correctly you will have created a fine looking topographic map similar to the one below. It’s also possible to create contours but that’s a tutorial for another day.

Wicklow-Topo

Technical note:

There are two hillshading algorithms available in QGIS, one by Horne (1981) and another by Zevenbergen and Thorne (1987). Jones (1998) examined the quality of hillshading algorithms, he found the algorithm of Fleming and Ho€er (1979) is slightly superior to Horne’s (1981) algorithm. Zevenbergen and Thorne’s (1987) algorithm is a derivation of Fleming and Ho€er’s (1979) formula. QGIS uses Horne’s (1981) algorithm by default.

References:

Horn, B.K., 1981. Hill shading and the reflectance map. Proceedings of the IEEE, 69, 14–47.

Jones, K.H., 1998. A comparison of algorithms used to compute hill slope as a property of the DEM [PDF]. Computers & Geosciences, 24, 315–323.

Zevenbergen, L.W. & Thorne, C.R., 1987. Quantitative analysis of land surface topography. Earth surface processes and landforms, 12, 47–56.

Nautical Charts in QGIS – The Compass Rose

Before the advent of shipborne satellite navigation systems, navigation at sea required three precise measurements – Solar or Stellar Declination for Latitude, Time at Greenwich for Longitude and True North that determined the ship’s heading. True North was obtained from the ship’s Magnetic Compass, an instrument who’s name indicates at an additional complication.

A magnetic compass does not point towards True North. Magnetic North is 100s km from the Geographic North Pole and the Earth’s magnetic field is uneven, it is distorted by magnetic irregularities within the Outer Core and intrinsically magnetic Mantle and Crustal rock. Additionally, the position of Magnetic North is not fixed, it is presently drifting from Arctic Canada towards Russia at 15 km per year. Therefore True North has to be derived from Magnetic North using a correction called Magnetic Declination (or Magnetic Variation), the angular difference between Magnetic North and True North. Magnetic Declination varies from location to location and over time.

Nautical navigation charts typically contain one or more Compass Roses, also called a Windrose, these consist of two circles – an outer circle that displays the cardinal directions of North, East, South and West and a inner circle that displays the direction of Magnetic North. The Magnetic Declination and its annual rate of change is typically printed within the Compass Rose, it is therefore possible to calculate the Magnetic Declination several years after a map is printed.

In this tutorial I will show you a process that to create a Compass Rose with the correct Magnetic Declination and Annual Rate of Change for any terrestrial location for use in QGIS. First we need to obtain a suitable Compass Rose graphic. Conveniently the United States National Oceanic and Atmospheric Administration (NOAA) published a Compass Rose in the Public Domain i.e. it is free to use without limitation. I downloaded a version of the NOAA Compass Rose from Wikimedia (or you can right click and save the Compass Rose below). Additionally, the background of this Compass Rose is transparent, this allows a map (or indeed a web page) to show though (note the Magnetic Declination in 1985 was 4 degrees 15 minutes west of True North and it had an annual decrease of 8 minutes of a degree per year).

800px-Modern_nautical_compass_rose.svg

There are several handy on-line utilities that can calculate Magnetic Declination and the Annual Rate of Change but we shall use Charles F. F. Karney’s excellent cross-platform GeographicLib in this case. GeographicLib is a suite of command line utilities for solving solving various geodesic problems such as conversions between geographic, UTM, UPS, MGRS, geocentric and local cartesian coordinates, gravity calculations, determining geoid height, and magnetic field calculations. The latest version can be obtained as a pre-compiled binary from Sourceforge or as source code.

The other essential step is to measure the precise map location in WGS84 coordinates. This can be done using the Coordinated Capture plug-in provided as standard with QGIS. To select the WGS84 coordinate reference system (CRS) click the sphere symbol in Coordinated Capture panel to open the Coordinate Reference System Selector. After setting the CRS to WGS84 (EPSG: 4326), click the icon left of the “Copy to Clipboard” button (this toggles real time display of captured coordinates) and then click “Start Capture”. The position in Decimal Degrees will be updated in the upper window as you move the cursor across the map, the lower window will display projected coordinates (in my case Pseudo Mercator EPSG: 3857). Clicking the map will select a coordinate point and the real time display will cease updating.

Wordpress

The MagneticField utility of GeographicLib is then used to calculate the Magnetic Declination and Annual Rate of Change for the captured coordinate, in this case a location east of Howth, Ireland.

$ MagneticField -r -t 2014-08-04 --input-string "53.37772 6.00935"

-3.57 67.81 18572.9 18536.9 -1152.2 45528.7 49171.3
0.17 -0.01 17.9 21.2 52.4 19.6 24.9

The results are: Magnetic Declination in degrees (-3.57); the inclination of the Magnetic Field in degrees (67.81); the horizontal strength of the magnetic field in nanotesla (18572.9 nT); the north component of the field (18536.9 nT); the east component of the field in (-1152.2 nT); the vertical component of the field in nT (45528.7 nT) and the total field (49171.3 nT). The numbers on the second line are the annual rate of change of these values, the first number is. We only need the first numbers on each line; the Magnetic Declination (-3.57) and Annual Rate of Change of Magnetic Declination (0.17). We can convert these to Degrees Minutes Seconds if required.

After calculating the Magnetic Declination and Annual Rate of Change, edit the NOAA Compass Rose in a graphics program such as  GIMP or Photoshop. In my case I copied the inner circle to a separate layer and I rotated it 3.57 degrees anticlockwise. I then added text to the Compass Rose stating the Magnetic Declination (Var.) and the Annual Rate of Change (Annual Decrease). After editing the Compass Rose graphic I finally added it to my Nautical Chart as a Image in Map Composer of QGIS.

Further Reading:

Bowditch, N. & ‎National Imagery and Mapping Agency, 2002. CHAPTER 3. NAUTICAL CHARTS. In: The American Practical Navigator: An Epitome of Navigation. Bethesda, MD : Washington, DC, Paradise Cay Publications, 9, 23–50. ISBN: 978-0939837540 http://msi.nga.mil/MSISiteContent/StaticFiles/NAV_PUBS/APN/Chapt-03.pdf


Adding ESRI’s Online World Imagery Dataset to QGIS

ESRI’s ArcGIS Online World Imagery is a high resolution satellite and aerial imagery base map for use in Google Earth, ArcMap and ArcGIS Explorer. The same excellent imagery is used by the Bing Maps Aerial layer. Somewhat surprisingly, World Imagery can also be accessed by QGIS, as it supports ESRI’s map servers that use Representational State Transfer (REST) and Simple Object Assess Protocol (SOAP) standards.

Simply copy and past the following code into the Python Console in QGIS and press return (Plugins – Console):

qgis.utils.iface.addRasterLayer("http://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer?f=json&pretty=true","raster")

The code adds an ESRI Online World Imagery base map to QGIS. It has a number of advantages over the popular OpenLayers Plugin that adds various Google, Bing and OpenStreetMap image layers to QGIS. Unlike images downloaded by the OpenLayers plugin the ESRI World Imagery base map is a true Raster who’s attributes are fully editable e.g. brightness, blending mode and transparency can be adjusted. World Imagery can also be printed at a very high resolution with other QGIS layers on a map and without it shifting relative to other layers; a conspicuous problem with OpenLayers that does not use “On the Fly” re-projection and only prints Google, Bing layers at a low resolution. It is an ideal aerial base map.

References:

QGIS: Adding An ArcServer Rest Service

Connecting to ArcGIS “mapserver” layers

Note: This method has been superseded by a plug-in that adds ESRI imagery and other REST layers via a GUI


The Coastal Vignette

Vignette2

Coastal Vignette seen on an old Irish ‘6-Inch map’

Occasionally on old maps you may see a pleasing decorative effect on bodies of water called a “Coastal Vignette”, these are fine lines that highlight coastlines and lake shores. The example seen above is from a ca. 100 year old “6-inch map” of Lough Nafooey in County Galway, Ireland. I presume the Coastal Vignette effect in this example was hand drawn, it required considerable skill and patience.

These is no plugin for creating Coastal Vignettes in QGIS just yet, so I developed a simple technique to recreate the effect using the raster Proximity (Raster Distance)’ algorithm accessible in the Processing Toolbox.

In order to use the Proximity Analysis tool I first converted a Shapefile polygon depicting the sea off Dublin into a 10 by 10 metre resolution Raster using the menu command ‘Raster – Conversion – Rasterize (Vector to raster)’.

Box

This generated a Raster that coded the Sea as ‘1’ (white) and ‘0’ (black) for Land.

Next, I selected ‘Proximity (raster distance)’  from the Processing Toolbox – (GDAL/OGR) – [GDAL] Analysis – Proximity (raster distance). You can quickly find the command by typing the algorithm’s name in the box above the Processing Toolbox.

Screenshot5

I entered 0 in the ‘Values’ box, this tells the Proximity algorithm to measure the distance away from land (a value of 0). The resulting Raster contains cell values that correspond to the distance away from the coast in metres, which I styled below.

The final step is to create Contours Lines from the Proximity analysis result using the menu item Raster – Contour. In my case I used an “interval between the contour lines” of 200 metres and I added an Attribute name called “DIST”.

Screenshot7

The resulting contour lines have distance attributes attached to them can be used to create a Graduated colour style if needed, though in my cause I manually edited the attributes of 10 contour lines nearest the coast and I gradually increased the transparency of the mid-grey contour lines from opaque at the coast to fully transparent out at sea. I made the remaining contour lines transparent.

And here is the finished result, with the Sea and an OpenStreetMap base map styled to look just like Google Maps.

Finished Vignette 2


Coordenadas dos cantos do mapa em QGIS | Map corner coordinates in QGIS

O desafio | The challenge

Em tempos na lista de discussão do qgis-pt alguém perguntou como dispor as coordenadas dos cantos do mapa no QGIS. Não estando (ainda) disponível tal funcionalidade, tentei chegar sem sucesso a uma solução que fosse de certa forma automática. Depois de remoer a ideia, e de ler um artigo do Nathan Woodrow, achei que a solução poderia passar por criar uma função para o construtor de expressões que pudesse ser usada em etiquetas no mapa.

Some time ago in qgis-pt mailing list, someone asked how to show the coordinates of a map corners using QGIS. Since this features wasn’t available (yet), I have tried to reach a automatic solution, but without success,  After some though about it and after reading a blog post by Nathan Woodrow, it came to me that the solution could be creating a user defined function for the expression builder to be used in labels in the map.

 A solução | The solution

Seguindo as indicações do referido artigo, comecei por criar um ficheiro userfunctions.py, que gravei na pasta .qgis2/python e, com uma ajuda do Nyall Dawson, escrevi o seguinte código.

Closelly following the blog post instructions, I have created a file called userfunctions.py in the  .qgis2/python folder and, with a help from Nyall Dawson I wrote the following code.

from qgis.utils import qgsfunction, iface
from qgis.core import QGis

@qgsfunction(2,"python")
def map_x_min(values, feature, parent):
 """
 Returns the minimum x coordinate of a map from
 a specific composer.
 """
 composer_title = values[0]
 map_id = values[1]
 composers = iface.activeComposers()
 for composer_view in composers():
  composer_window = composer_view.composerWindow()
  window_title = composer_window.windowTitle()
  if window_title == composer_title:
   composition = composer_view.composition()
   map = composition.getComposerMapById(map_id)
   if map:
    extent = map.currentMapExtent()
    break
 result = extent.xMinimum()
 return result

Depois de correr o comando import userfunctions na consola python (Módulos > Consola python), já conseguia usar a função map_x_min() (disponível na categoria python) numa expressão para obter o valor mínimo em X.

After running the command import userfunctions in the python console  (Plugins > Python Console), it was already possible to use the  map_x_min() function (from the python category) in an expression to get the minimum X value of the map.

Screenshot from 2014-09-09 16^%29^%29
Bastava então criar as restantes funções map_x_max(), map_y_min() e map_y_max(). Como parte do código seria repetida, decidi encapsulá-lo na função map_bound() que recebesse como argumentos o título do compositor de impressão e o id do mapa e me devolvesse a extensão do mesmo (sob a forma de um QgsRectangle).

All I needed now was to create the other three functions,  map_x_max(), map_y_min() and map_y_max().  Since part of code would be repeated, I have decided to put it in a function called map_bound(), that would use the print composer title and map id as arguments, and return the map extent (in the form of a QgsRectangle).

from qgis.utils import qgsfunction, iface
from qgis.core import QGis

def map_bounds(composer_title, map_id):
 """
 Returns a rectangle with the bounds of a map
 from a specific composer
 """
 composers = iface.activeComposers()
 for composer_view in composers:
  composer_window = composer_view.composerWindow()
  window_title = composer_window.windowTitle()
  if window_title == composer_title:
   composition = composer_view.composition()
   map = composition.getComposerMapById(map_id)
   if map:
    extent = map.currentMapExtent()
    break
 else:
  extent = None

 return extent

Com essa função disponível podia usá-la internamente nas funções para devolver cada um dos mínimos e máximos em X e Y, tornando o código mais compacto e fácil de manter. Adicionei ainda ao código original alguns mecanismos para evitar erros.

With this function available, I could now use it in the other functions to obtain the map X and Y minimum and maximum values, making the code more clear and easy to maintain. I also add some mechanisms to the original code to prevent errors.

@qgsfunction(2,"python")
def map_x_min(values, feature, parent):
 """
 Returns the minimum x coordinate of a map from a specific composer.
 Calculations are in the Spatial Reference System of the project.<br>
 <h2>Syntax</h2>
 <p>map_x_min(composer_title, map_id)</p>
 <h2>Arguments</h2>
 <p>composer_title - is string. The title of the composer where the map is.<br>
 map_id - integer. The id of the map.</p>
 <h2>Example</h2>
 <p>map_x_min('my pretty map', 0) -> -12345.679</p>
 """
 composer_title = values[0]
 map_id = values[1]
 map_extent = map_bounds(composer_title, map_id)
 if map_extent:
  result = map_extent.xMinimum()
 else:
  result = None

 return result

@qgsfunction(2,"python")
def map_x_max(values, feature, parent):
 """
 Returns the maximum x coordinate of a map from a specific composer.
 Calculations are in the Spatial Reference System of the project.<br>
 <h2>Syntax</h2>
 <p>map_x_max(composer_title, map_id)</p>
 <h2>Arguments</h2>
 <p>composer_title - is string. The title of the composer where the map is.<br>
 map_id - integer. The id of the map.</p>
 <h2>Example</h2>
 <p>map_x_max('my pretty map', 0) -> 12345.679</p>
 """
 composer_title = values[0]
 map_id = values[1]
 map_extent = map_bounds(composer_title, map_id)
 if map_extent:
  result = map_extent.xMaximum()
 else:
  result = None

 return result

@qgsfunction(2,"python")
def map_y_min(values, feature, parent):
 """
 Returns the minimum y coordinate of a map from a specific composer.
 Calculations are in the Spatial Reference System of the project.<br>
 <h2>Syntax</h2>
 <p>map_y_min(composer_title, map_id)</p>
 <h2>Arguments</h2>
 <p>composer_title - is string. The title of the composer where the map is.<br>
 map_id - integer. The id of the map.</p>
 <h2>Example</h2>
 <p>map_y_min('my pretty map', 0) -> -12345.679</p>
 """
 composer_title = values[0]
 map_id = values[1]
 map_extent = map_bounds(composer_title, map_id)
 if map_extent:
  result = map_extent.yMinimum()
 else:
  result = None

 return result

@qgsfunction(2,"python")
def map_y_max(values, feature, parent):
 """
 Returns the maximum y coordinate of a map from a specific composer.
 Calculations are in the Spatial Reference System of the project.<br>
 <h2>Syntax</h2>
 <p>map_y_max(composer_title, map_id)</p>
 <h2>Arguments</h2>
 <p>composer_title - is string. The title of the composer where the map is.<br>
 map_id - integer. The id of the map.</p>
 <h2>Example</h2>
 <p>map_y_max('my pretty map', 0) -> 12345.679</p>
 """
 composer_title = values[0]
 map_id = values[1]
 map_extent = map_bounds(composer_title, map_id)
 if map_extent:
  result = map_extent.yMaximum()
 else:
  result = None

 return result

As funções ficaram disponíveis no construtor de expressões na categoria “Python” (podia ter-lhe dado outro nome qualquer) e as descrições das funções são transformadas em textos de ajuda para fornecer ao utilizador informação de como utilizar as funções.

The functions became available to the expression builder in the “Python” category (could have been any other name) and the functions descriptions are formatted as help texts to provide the user all the information needed to use them.

Screenshot from 2014-09-09 15^%39^%19

Usando as funções recentemente criadas, foi fácil posicionar etiquetas  junto dos cantos do mapa com as coordenadas dos mesmos. Qualquer alteração à extensão do mapa, reflecte-se nas etiquetas, podendo por isso ser usadas convenientemente com a funcionalidade de atlas.

Using the created functions, it was now easy to put the corner coordinates in labels near the map corners. Any change to the map extents is reflected in the label, therefore quite useful to use with the atlas mode.

Screenshot from 2014-09-09 15^%40^%27

O resultado destas funções pode ser usado com outras. Na imagem seguinte apresenta-se uma expressão para apresentar as coordenadas de forma mais compacta.

The functions result can be used with other functions. In the following image there is a expression to show the coordinates in a more compact way.

Screenshot from 2014-09-09 15^%43^%55

Havia um senão… Para as funções ficarem disponíveis, seria necessário importá-las manualmente em cada utilização do QGIS. Algo que não era prático. Novamente com a ajuda do Nathan, fiquei a saber que podemos importar módulos Python no arranque do QGIS colocando na pasta .qgis2/python um ficheiro com o nome startup.py com os comandos de importação. Para o meu caso bastou o seguinte.

There was a setback… For the functions to become available, it was necessary to manually import them in each QGIS session. Not very practical. Again with Nathan’s help, I found out that it’s possible to import python modules at QGIS startup by putting a startup.py file with the import statements in the .qgis2/python folder. In my case this was enough.

import userfunctions

Conclusões | Conclusions

Fiquei bastante satisfeito com o resultado. A possibilidade do utilizador criar as usas próprias funções para usar em expressões vem mais uma vez demonstrar como é fácil personalizar e criar as minhas próprias ferramentas para QGIS. Já estou a matutar em mais aplicações para estar fantástica funcionalidade.

I was pretty satisfied with the end result. The ability to create your own functions in expressions demonstrates once more how easy it is to customize QGIS and create your own tools. I’m already thinking in more applications for this amazing functionality.

UT 9 - Qta da Peninha - Vegetação potencial

Os ficheiros Python com as funções criadas podem ser descarregados AQUI. Basta descompactar os dois ficheiros para a pasta .qgis2/python e reiniciar o QGIS, e as funções devem ficar disponíveis.

You can download the Python files with the functions HERE. Just unzip both files to the .qgis2/python folder, and restart QGIS, and the functions should become available.

Disclaimer: I’m not an English native speaker, therefor I apologize for any errors, and I will thanks any advice on how to improve the text.


Profile Tool tutorial

Profile Tool is a plugin for QGIS which makes it possible to generate (elevation) profiles for line features. The plugin is available through the default QGIS plugin repository. While testing the plugin, I found some aspects of using the tool might require additional instructions.

After installing and enabling the plugin, you will find the “Terrain profile” button in the plugin toolbar:

qgisprofiletool

The basic use case is as follows:

  1. Load the elevation raster and select this raster layer in the layer list.
  2. Press the “Terrain profile” button. This opens the plugin panel which consists of a graph area on the left and a raster layer list on the right. The raster layer you had selected will be added to the raster layer list.
  3. If you have “Selection: Temporary polyline” enabled, you can now draw a line in the map area. Double-click left to end drawing the line. (If you are paying close attention, you might have noticed the instructions in the status bar.)
  4. After you have finished drawing the line, the graph area will update and display the profile.

qgisprofiletool2

If you want to add another raster layer to the plugin, you need to first select the raster layer in the QGIS layer list and then press the “Add Layer” button in the Profile Tool panel.

To generate the profile for an existing line feature, you need to change the selection mode from “Temporary polyline” to “Selected polyline”. Then you need to select the vector layer which contains the line feature you want to use in the QGIS layer list. Finally, you can click on the line feature in the map area to select it. (Note that this selection is independent of any selections you might have going on using the default QGIS feature selection tools.)

If you change from the Profile Tool to any other tool such as “Pan Map” or “Identify”, you have to click the “Terrain profile” button again to re-enable drawing/selection a line for the Profile Tool.

Due to a bug, it is currently not possible to export the profile graph. An alternative is to open the “Table” tab of the Profile Tool panel which provides access to the profile data and copy the data into your preferred graphing application such as Calc or Excel.

If you want to see the Profile Tool in action, I recommend watching the introduction video by Lene Fischer (University of Copenhagen).


Group Stats Tutorial

Group Stats is a plugin for QGIS which makes it easy to calculate statistics for feature groups in a vector layer. Note that the plugin is still marked “experimental” so you have to allow experimental plugins in order to install it. I tried this plugin for the first time today and decided to write this post because it didn’t seem immediately obvious how to use it.

The plugin button is added to the vector toolbar and of course you can access it via vector menu.

groupstatsicon

The example I want to show is: How to calculate the total area of of each Corine Land Cover (CLC) class per state.

corineAT

After adding state information to the CLC datasets by intersecting CLC and state geometries from Natural Earth we can get started with Group Stats.

groupstats

The big area on the left will display the results. The input fields are on the right. The general idea is to drag and drop fields and/or functions into the “columns”, “rows” and “values” sections. (Double-clicking field names does not do anything.) To remove fields again, you have to drop them back into the field list.

To calculate the total area of of each Corine Land Cover (CLC) class per state, I chose land cover classes as columns, state names as rows and sum of areas as values:

groupstatsclc

It’s also possible to add multiple functions in the columns/rows input sections to calculate different statistics at once:

groupstats_functions

Group Stats can be used in many cases that otherwise require a Spreadsheet software. The results can be exported to CSV easily. Usability could certainly be improved by allowing common interactions such as removing fields by pressing the delete key or adding fields by double-clicking.


QGIS Video Tutorials

QGIS wiki now has it’s own section listing QGIS video tutorials.
If you know of any tutorials not listed yet, leave a comment and I’ll add them.

Together with the newly started “How to I do that in QGIS” tutorial collection, this will hopefully become the number one reference for both new users doing their first GIS-related work and advanced uses interested in the latest QGIS features.


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