A QGIS project is the working area where it is possible handle geographic data and then performing digitalization, editing, querying, spatial analyses.
In all GIS desktop software the most part of the data operations are performed into a specific project.
The GIS project is a collection of geographic data (also known as feature classes) which, as they are added in the project, they become GIS layers.
Each layer has specific properties, for example: a name (can be different from the name of the correspondent geographical datum), a cartographic reference system (CRS), a symbolization style and transparency for an optimal visualization. The project too has some specific properties, including its CRS, unit of measure, etc..
In this tutorial you will practice in creating a GIS project and in settings the project and layers properties.
1. Open QGIS. As you open QGIS, by default, a blank project will appear. If QGIS has just been installed, several toolbars and panels will be loaded in the project. Probably you do not need of many of them, hence it is necessary to remove them in order to optimize the interface.
2. Adding/removing toolbars. Go to View menu, move the mouse on the Toolbars item and the list of available toolbars will open. Click on the toolbar and/or panel check boxes that you want to add/remove from the main window of QGIS.
3. Save the project. It is advisable to save and name the project that you are creating. You can save it in your file system or in the local network. QGIS projects file has. qgs extension. To save it, click on Project menu and then Save or Save As options (a suggestion: create a working folder where you will save all the data that you will produce ).
4. Set CRS. A good practice is to load in the project geographic data having the same coordinate reference system and use that as CRS of the project. Otherwise, if you need to load geographic data with different CRS, QGIS will execute a CRS transformation “on the fly”, in order make possible the overlapping of all layers in the project. For setting the CRS, click on menu Project and Project Properties option. Following window will appear:
Click on “Enable ‘on the fly’ CRS transformation” and in the “Coordinate reference systems of the world” table, browse the CRS that we chose as working CRS: WGS84 – UTM 33N. In the aforesaid table, all CRSs are gathered into two general groups: Geographic Coordinate Systems (lat-long CRSs) and Projected Coordinate Systems (planar CRSs). The WGS84-UTM33N is:
5. Loading vector data. It is possible to load into a QGIS project different kinds of vector geographic data; for example: Shapefile, Esri file geodatabase, SpatialLite geodatase, furthermore it is possible to access to geographic databases as Oracle, MSSQL, PostGIS.
In this tutorial we will use shapefile only; to load a shapefile, follow this procedure:
- go to menu Layer -> Add Layer -> Add Vector Layer and the follow window will appear:
- in “Source type” select “File” and then click on the “Browse” button to choose the shapefile that you want to add to the project;
- select the shapefile containing the municipalities in L'Aquila province:
... \QGIS course\Data\com_laquila_wgs84utm33. shp
What is the geometric primitive of the shapefile just added? (2)
You can see the map in the canvas area and the name of the layer in table of content, where it is possible to make visible or invisible the layer by clicking in the check box beside the name of the layer (red square).
By using the same procedure, add to the project the following vector data:
... \QGIS course\Data\urban_laquila_wgs84utm33. shp
... \QGIS course\Data\roads_osm_laquila_wgs84utm33. shp
6. Zoom, pan and zoom to layer. Some map navigation tools are available for zooming and panning the map in the canvas area:
Try different kinds of zoom and pan.
7. Open attribute table and execute a simple selection. Each vector layer has an attribute table where non geographic information are stored. Open the attribute table by right-clicking on the name of layer in TOC and in the context menu click “Open Attributes Table”. This table will appear:
You can see the fields (attributes) and the records (objects or features). Moreover, the table contains further information, including the total number of records and a toolbar having tools to execute queries, calculations and other operations.
Select one record by clicking on the number on the left (red box in the screenshot below) and observe what happen in the map.
Now, select one feature directly on the map view, but before take a look to following toolbar:
By using the button “select feature (s) ” (A), select a polygon on the map, open the attribute table of the layer (you can use also the button D) and observe the changing in the table (Select Features button operates on the selected layer in the TOC).
8. Identifying features. It is very useful retrieving quickly attribute data from objects, without performing a selection (the selection is very important for many other functions). To do that you can use the button “Identify Features”. After having pressed this button, click on one polygon and a new panel will appear:
In that panel, you can see attribute data and some geometric data (in the Derived section).
Retrieve information about the easternmost municipality of the L'Aquila province: what is the name? (3). What is its area? (4).
9. Measure tool. This tool permits to execute quick measurements. It is possible to perform linear, areal and angular measurements. It is necessary to take into account that results can be imprecise, because: i) the position of starting/intermediate/end points that you pick on the map is not precise; ii) the measurement is affected by the cartographic error, depending on the cartographic reference system used.
Follow these steps for execute a linear measurement:
- click on Measure dropdown menu (down arrow) to select the kind of measure;
- select Measure Line;
- on the map, left-click first and intermediate points and right-click to pick the last point of the segment; in the Measure window will be shown the result.
10. Loading raster data. Likewise for vector data, QGIS is able to load many raster formats, including: tiff, jpg, ESRI grid, ecw and many others. The loading operation is similar to what you have already seen for vector data. Go to menu Layer -> Add Layer -> Add Raster Layer and browse in the dialog window to search the raster that you want to load into the project. Search in the data folder the raster “hill_srtm85. tif”:
... \QGIS course\Data\hill_srtm85. tif
It is a hillshade layer that gives a picture of the relief of the area, simulating a 3D view. Usually, a hillshade derives from a Digital Elevation Model (DEM) after a simple raster operation.
11. Arrange layers in the TOC. By moving up or down (using drag & drop) a layer in the TOC it is possible modify the order of visibility of the layers.
Move layers in order to make completely visible the municipalities layer.
By right-clicking on the layer, it is possible to rename, remove and execute other operations on the layer.
For now, rename the raster hill_srtm85 and give it a different name.
12. Load other layers. By applying the procedures described up to now, on your own, load some vectors that you can find in the data folder and explore their properties, attribute tables, etc.. Do some operations, including: moving up and down layers in the TOC, renaming, removing.
13. Setting the transparency. You will have noticed that it is impossible to make visible simultaneously two full-coverage layers, for example, municipalities and hillshade layers. In order to try to overcome this problem, it is possible to make partially transparent one layer. In this case, a good strategy could be to visualize the hillshade with a 50% transparency. To do that, go to layer properties → tab Transparency and in the frame Global Transparency move the sliding bar to select the desired transparency value.
For vector layer, the transparency setting is in properties window → tab Style (bottom part of the window).
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A QGIS project is the working area where it is possible to handle geographic data and then to perform digitalization, editing, querying and spatial analyses.
In every GIS desktop software, most part of the data operations is performed into a specific project.
The GIS project is a collection of geographic data (also known as feature classes) which, after being added in the project, becomes GIS layers. (becomes = referred to "collection")
Each layer has specific properties, for example: a name (can be different from the name of the correspondent geographical datum), a cartographic reference system (CRS), a symbolization style and transparency for an optimal visualization. The project too has some specific properties, including its CRS, unit of measure, etc..
Through this tutorial, you will practice in creating a GIS project, and through the settings, the project and layers' properties.
1. Open QGIS. As you open QGIS, by default, a blank project will appear. If QGIS has just been installed, several toolbars and panels will be loaded in the project. Probably you do not need any of them, hence it is necessary to remove them in order to optimize the interface.
2. Add/remove toolbars. Go to View menu, move the mouse to the Toolbars item and the list of available toolbars will open. Click on the toolbar and/or panel check boxes that you want to add/remove from QGIS main window
3. Save the project. It is advisable to save and name the project that you are creating. You can save it in your file system or in the local network. QGIS projects file has. qgs extension. To save it, click on Project menu and then Save or Save As options (a suggestion: create a working folder where you will save all the data that you will produce ).
4. Set CRS. A good practice is to load in the project's geographic data by having the same coordinate reference system and use that as CRS of the project. Otherwise, if you need to load geographic data with different CRS, QGIS will execute a CRS transformation “on the fly”, in order to make possible the overlapping of all layers in the project. For setting the CRS, click on menu Project and Project Properties option. The following window will appear:
Click on “Enable ‘on the fly’ CRS transformation” and in the “Coordinate reference systems of the world” table, browse the CRS that we chose as working CRS: WGS84 – UTM 33N. In the aforesaid table, all CRSs are gathered into two general groups: Geographic Coordinate Systems (lat-long CRSs) and Projected Coordinate Systems (planar CRSs). The WGS84-UTM33N is:
5. Loading vector data. It is possible to load into a QGIS project different kinds of vector geographic data; for example: Shapefile, Esri file geodatabase, SpatialLite geodatase, furthermore it is possible to access to geographic databases as Oracle, MSSQL, PostGIS.
In this tutorial we will use shapefile only; to load a shapefile, follow this procedure:
- go to menu Layer -> Add Layer -> Add Vector Layer and the following window will appear:
- in “Source type” select “File” and then click on the “Browse” button to choose the shapefile that you want to add to the project;
- select the shapefile containing the municipalities in L'Aquila province:
... \QGIS course\Data\com_laquila_wgs84utm33. shp
What is the geometric primitive of the shapefile just added? (2)
You can see the map in the canvas area and the name of the layer in table of content, where it is possible to make the layer visible or invisible by clicking in the check box beside the name of the layer (red square).
By using the same procedure, add to the project the following vector data:
... \QGIS course\Data\urban_laquila_wgs84utm33. shp
... \QGIS course\Data\roads_osm_laquila_wgs84utm33. shp
6. Zoom, pan and zoom to layer. Some map navigation tools are available for zooming and panning the map in the canvas area:
Try different kinds of zoom and pan.
7. Open attribute table and execute a simple selection. Each vector layer has an attribute table where non geographic information is stored. Open the attribute table by right-clicking on the name of the layer in TOC and in the context menu click “Open Attributes Table”. This table will appear:
You can see the fields (attributes) and the records (objects or features). Moreover, the table contains further information, including the total number of records and a toolbar having tools to execute queries, calculations and other operations.
Select one record by clicking on the number on the left (red box in the screenshot below) and observe what happens in the map.
Now, select one feature directly on the map view, but before take a look to the following toolbar:
By using the button “select feature (s) ” (A), select a polygon on the map, open the attribute table of the layer (you can also use the button D) and observe the changing in the table (Select Features button operates on the selected layer in the TOC).
8. Identifying features. It is very useful retrieving quickly attribute data from objects, without performing a selection (the selection is very important for many other functions). To do that, you can use the button “Identify Features”. After having pressed this button, click on one polygon and a new panel will appear:
In that panel, you can see attribute data and some geometric data (in the Derived section).
Retrieve information about the easternmost municipality of the L'Aquila province: what is the name? (3). What is its area? (4).
9. Measure tool. This tool allows to execute quick measurements. It is possible to perform linear, areal and angular measurements. It is necessary to take into account that results can be imprecise, because: i) the position of starting/intermediate/end points that you pick on the map is not precise; ii) the measurement is affected by the cartographic error, depending on the cartographic reference system used.
Follow these steps to execute a linear measurement:
- click on Measure dropdown menu (down arrow) to select the kind of measure;
- select Measure Line;
- on the map, left-click first and intermediate points and right-click to pick the last point of the segment; in the Measure window, the following result will be shown:
10. Loading raster data. Likewise for vector data, QGIS is able to load many raster formats, including: tiff, jpg, ESRI grid, ecw and many others. The loading operation is similar to what you have already seen for vector data. Go to menu Layer -> Add Layer -> Add Raster Layer and browse in the dialogue window to search for the raster that you want to load into the project. Search in the data folder the “hill_srtm85. tif” raster:
... \QGIS course\Data\hill_srtm85. tif
It is a hillshade layer that gives the picture a relief of the area, simulating a 3D view. Usually, a hillshade derives from a Digital Elevation Model (DEM) after a simple raster operation.
11. Arrange layers in the TOC. By moving up or down (using drag & drop) a layer in the TOC it is possible to modify the order of visibility of the layers.
Move layers in order to make the municipalities layer completely visible.
By right-clicking on the layer, it is possible to rename, remove and execute other operations on the layer.
As for now, rename the raster hill_srtm85 and give it a different name.
12. Load other layers. By applying the procedures described up to now, on your own, load some vectors that you can find in the data folder and explore their properties, attribute tables, etc.. Do some operations, including: moving up and down layers in the TOC, renaming, removing.
13. Setting the transparency. You will have noticed that it is impossible to make simultaneously visible two full-coverage layers, for example, municipalities and hillshade layers. In order to try to overcome this problem, it is possible to make one layer partially transparent. In this case, a good strategy could be to visualize the hillshade with a 50% transparency. To do that, go to layer properties → tab Transparency and in the Global Transparency frame move the sliding bar to select the desired transparency value.
For vector layer, the transparency setting is in properties window → tab Style (bottom of the window).
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