Geodata management#

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In this chapter, we will have a close look at how to work with geodata in QGIS. Since vector data is the primary geodata type you will work with at the beginning of your GIS career, we will focus on vector geodata. We will learn how to set up a coherent folder structure for your GIS-data and projects and how to name geodata correctly.

Fundamentals of Geodata Management#

Working with geodata is not like working with data in programs such as Microsoft Excel or Word. Whenever you load an image in a Word file, the file will contain the image. If you delete the image on your computer, the Word file will still contain a copy of the image.

This is not the case in QGIS! When you load geodata into QGIS, the system only establishes a link to the location where the data is stored on your computer. This means your QGIS project does not contain the geodata, it only links to it. If you load data in your QGIS project and you change the location of the data or delete it, the data is no longer available in your QGIS project and you will get an error when you open it.

Because you are working directly with the source data, rather than a copy, whenever you edit data in QGIS the changes replace the source data and can not be reversed. If you plan to make changes to your data, you should make a copy of it first so that you always have a ‘clean’ copy you can go back to.

Standard folder structure#

The single most important geodata management practice is to use a standardised folder structure that contains all parts of the QGIS project.

The paths from a QGIS project to the geodata are by default relative. This means when the data and the project are in a fixed folder structure, you can move the whole structure without impacting the QGIS project or the paths to the data. The version of a standardized folder structure that is used for all exercises in this training is explained below. A template of the folder structure can be downloaded here.

A standard folder structure has two principal advantages:

  1. If we share the whole project folder, we can expect the project to run without problems on a different computer

  2. The folder structure supports the proper organisation of project data and helps ensure the QGIS project will work as intended

../../_images/Standard_project_folder_structure.drawio.svg

Fig. 36 Standard folder structure. Source: HeiGIT#

Naming Geodata#

Naming your data correctly ensures that you can identify the layers and your computer does not run into any issues when working with your data files. The name of your files themselves need to be clear, meaning that you or others can identify what the data shows, where the data comes from, and to what time it refers. In QGIS, you should name your layers so you can identify the content, as well as what you have done with the layer. For example, if you have clipped a street layer of new york, do not name the layer “clipped”, give it a name such as “streets_NYC_clipped”.

There are some basic principles when it comes to naming geodata that you produce or manipulate:

  • Do not use special characters like !,?, / or -.

  • Do not use blank spaces, use underscores _

  • Give layers meaningful names so that you can understand what they represent, even if they are a temporary/intermediate step in a workflow.

Below you can see an example of a workflow to process an admin boundary dataset (adm0). The purpose of the intermediate steps is not clear because the layer names are not meaningful.

adm0 >> adm0_temp >> adm0_temp2 >> adm0_temp3 >> facilities_final

A good naming system for layers is shown below. In this workflow, it is clear what processing was performed at each step (reproject, clip layer, join with another layer, final result).
In this way, other people can understand what purpose different layers serve and whether they are needed in the final project.

adm0 >> adm0_projUTM >> adm0_projUTM_clipUrban >> adm0_projUTM_clipUrban_intersectFacilities >> facilities_processed