Introduction to QGIS 3: Data collection and Management (Chapter 3)

First, however, we will deal with the general recording of values in tables. A table consists of rows and columns. The row is horizontal and the different datasets are stored in it. The column is vertical and a certain property of a data set is stored in it.

Tables are often used to store values from measurements. For example, the number of students in a class can be stored in a table. The number of students of a class can be counted. In addition, the class teacher could also be entered in the table. The corresponding table would then look as follows.

The names of the columns (e.g. class, number of students…​) are called attributes.

For geodata, the geometry must also be saved in addition to the attributes. In the previous exercises you already got to know the shapefile as a storage type for geodata. With the Shapefile, the geometry and the attribute data are saved in different files.

Open the directory in which the data for the exercise is stored and take a closer look at the data. In addition to the main file with the extension .shp there are other files with the same name but a different extension. For example, the file with the extension .dbf contains the factual data and the file with the extension .prj contains the coordinate system. All these files together form the shape file.

The geodata can also be stored in special databases, so-called geodatabases. These databases function similarly to normal databases, but additionally offer the possibility to manage geometry as well as factual information. Normal databases cannot do this. Examples for geo databases are e.g. Oracle Spatial and PostGIS.

Now you have learned in which form geodata can be saved. But how do you get from the objects in the real world to the information you want to store?

Task 1
Think for two to three minutes about what sources the data might come from and what collection methods you know. Continue in the text only then.

There are many methods to capture geodata. We would like to briefly discuss some of them.

Data acquisition and management usually takes a lot of time. But the effort is worth it, because the data can be regarded as the core of the GIS. If the quality of the data is poor or the data is incomplete or outdated, the results of the evaluations or the maps created from the data are correspondingly poor.

Compared to the other GIS components software and hardware, the data have a very long service life. While better and faster computers are coming onto the market and the software products are usually outdated after a few years, the data can be used for decades.

Since the collection is very complex, one is naturally also interested in being able to use the data as long as possible. In order to guarantee this, regular updating is just as important as good and clean data collection. The principle "as accurate as possible" does not apply to the collection of data, but "as accurate as necessary".

When you’ve solved the exercise, you’ve learned the following:

The location of the cantonal capitals is stored in the text file Hauptorte.txt. Open this file in a text editor and take a closer look at the content.

Task 2
In what form is the location of them stored in locations and how is the information separated from each other? Write your findings on your worksheet.

The Add Delimited Text Layer tool for reading coordinates from a text file can be found in the Manage Layers Toolbar toolbar. If you don’t know how to show toolbars anymore, have a look at chapter 1 again.

Open the new tool and first enter the type of separator that separates the information in the text file (see Result of the last task).

Then click on the …​ button and select the text file Hautporte.txt. The tool now automatically divides the text file into different fields, whereby the selected separator determines where the new field begins.

Below the geometry a suggestion appears automatically, which field should be used as X-field and which as Y-field. Compare the suggestion with your considerations. If you don’t agree, change the entry. Then click on the OK button to display the main locations in the project.

In order to be able to perform spatial analyses with the new Layer Main Locations later, the same coordinate reference system as the other layers must be assigned to the Layer. Open the Layer Properties of the main locations and search under Source: the correct CRS/KBS. Select the coordinate system CH1903 /LV03 with the EPSG-No. 21781.

If you now open the attributes table, you will see the information of the text file displayed in a table. Additionally a position in the map was calculated from the selected numbers for the X- and Y-coordinates and a point was placed there.

Now the main locations are to be labelled. Open the Layer Properties window and select the Labels option. For Show labels select the Single Labels field and as Description field select the field with the name Main. Then adjust the font size, placement, clipping, etc. until the label fits "into the image". In addition, select more suitable point symbols for the main locations.

A new tool introduced in QGIS 3 is the Locator Bar.

In QGIS, the Locator Bar can be opened with the keyboard shortcut Ctrl + K.

With the Locator Bar you can search for actions, "computers" (calculation operations), processing algorithms and much more from QGIS.

Try the tool yourself by selecting the lakes layer and searching for a lake in the Locator Bar. Use the prefix f for the search.

Example: f Greifensee

You can find the prefixes by opening the locator with Ctrl + K, or under Settings → Options…​ → Locator

In addition to the existing lakes, two further lakes are now to be included: the Lungernsee and the Wägitalersee.

To capture the Lungernsee, zoom near Sarnen. The lake between Giswil, Brienz and Meiringen is the Lungernsee. In order to collect data at all, the layer must be marked with the lakes and the Toggle Editing button must be selected from the Digitizing Toolbar toolbox. The same is done by right-clicking on the layer and then selecting the Toggle Editing option. Try both methods and decide which one you want to use in the future.

The buttons that can be used for digitizing are now activated. Select the Add Polygon Feature button and place points along the light blue line of the shore area on the map. To close the area press the right mouse button. A window appears automatically in which the attributes can be entered. Enter the following values:

Name: Lungernsee; Type: Speichersee;

Area: 2.01 km²; Height: 688.0 meters above sea level; Depth: 68 m; Volume: 0.065 km³

As already mentioned, the second lake to be covered is called Lakeägitalersee and lies between Lake Sihl, Lake Zurich and the village of Glarus. Also record the geometry and attributes of this lake. Here some more information:

Name: Wägitalersee; Type: Speichersee;

Area: 4.18 km²; Height: 900.0 meters above sea level; Depth: 65 m; Volume: 0.150 km³

To save the changes, the editing status must be changed again. As long as you do not do this, the data you have entered will not be saved.

Congratulations, you have captured your first objects yourself with QGIS!

Vector data can be stored in different forms.

What two species do you know?

Write an additional sentence for each form in which you name a special feature.

It is not only in a GIS that information is often stored in the form of a table.

How would you describe the structure of such a table to someone who has never seen one before?

You may also use a sketch to answer this question. The important terms, however, must be written in your answer.

One way to store information about objects is to write them into a text file.

Answer the questions in your own words and justify your answers. Think back to the exercise when answering the questions.

Your class teacher will instruct you to create a GIS for your next school trip, in which the various intermediate stations of the trip and the hiking route are spatially represented.

What possibilities do you have to get the different dates?

Select two topics that you would like to present in the School Travel GIS. Answer the question for both topics. However, two different entry types must be described. There are several correct ways.