Open Source Desktop GIS

Quantum GIS (QGIS) Complete Guide

Master QGIS, the world's leading free open-source desktop Geographic Information System desktop suite.

1. QGIS Desktop Suite Installation

QGIS is free software compiled for all operating systems. Always use the **LIT (Long Term Release)** version to guarantee stability for academic research workflows.

Windows Installation

Download the standard `.msi` 64-bit standalone installer from the official QGIS portal (qgis.org) and click through the setup wizard.

macOS Installation

Download the `.dmg` packages. Open the disk image and drag QGIS to your Applications directory.

Linux (Ubuntu/Debian) Command Line Setup

To acquire the latest LTR build on Debian-based platforms, execute the following commands in your shell:

Bash Shell 
# Update packages list and install prerequisite utilities
sudo apt update
sudo apt install gnupg software-properties-common

# Import GPG key and add official QGIS LTR repository
sudo mkdir -m755 -p /etc/apt/keyrings
sudo wget -O /etc/apt/keyrings/qgis-archive-keyring.gpg https://download.qgis.org/downloads/qgis-archive-keyring.gpg

# Install QGIS along with python extensions and GRASS provider
sudo apt update
sudo apt install qgis qgis-plugin-grass python3-qgis

2. Working with Vector Layers

Vectors represent spatial targets as discrete objects (Points, Lines, Polygons). To load a vector layer in QGIS:

  1. Go to Layer > Add Layer > Add Vector Layer.
  2. Click the browse button under Source, locate your `.shp` (Shapefile) or `.geojson` file, and click Add.
  3. Right-click the loaded layer in the Layers panel and choose Properties > Symbology.
  4. Under Symbology, choose Categorized or Graduated (for numeric attributes) to style boundaries with a color ramp, adjusting transparency and borders as needed.

3. Raster Composites & Elevation Models

Rasters represent continuous grids of cell values (e.g., satellite imagery bands, Digital Elevation Models). To import a Digital Elevation Model (DEM) GeoTIFF file:

  1. Go to Layer > Add Layer > Add Raster Layer and load the `.tif` file.
  2. Right-click the layer and choose Properties > Symbology.
  3. Under Render type, select Singleband pseudocolor.
  4. Select a clean elevation color ramp (e.g. green-to-brown) and click **Classify** to divide elevation heights into visible color steps.

4. Georeferencing Scanned Paper Maps

Paper maps or old sketches do not have coordinate projections. Georeferencing is the process of aligning scanned images with real-world spatial coordinates:

  1. Go to Layer > Georeferencer.
  2. Click the Open Raster button and load your scanned paper map (`.jpg` or `.png`).
  3. Examine your paper map for grid intersections showing coordinate annotations. Click on an intersection and input the coordinate values (Latitude/Longitude or Easting/Northing). These points are known as **Ground Control Points (GCPs)**.
  4. Collect at least 4 widely spaced GCP points.
  5. Open **Transformation Settings**. Select the **Polynomial 1** transformation type, the **WGS 84 / UTM zone** target CRS, and name your output GeoTIFF. Click the green play button to georeference your map!

5. Cartographic Print Layout Composer

Once your vector and raster styles are fully designed, you must compile them into a professional map with appropriate marginalia for publication:

  1. Go to Project > New Print Layout and input a descriptive title (e.g., "Study Area Location Map").
  2. Click **Add Map** and draw a rectangle across the canvas to display your spatial layers.
  3. Click **Add Legend** to place a dynamic symbol guide. Uncheck "Auto update" in the item properties to clean up and rename layer elements manually.
  4. Use **Add Scale Bar** and **Add North Arrow** buttons to place crucial cartographic scaling and orientation indicators.
  5. Go to Layout > Export as PDF or Export as Image to export your map for inclusion in dissertations or research publications.

6. Essential Plugins (SCP & QuickMapServices)

Plugins add advanced functionality to the base QGIS software. To install plugins, go to **Plugins > Manage and Install Plugins**:

  • QuickMapServices (QMS): Instantly adds high-resolution base maps (Google Satellites, Esri Terrain, OpenStreetMap) beneath your shapefiles. Once installed, access them under **Web > QuickMapServices**.
  • Semi-Automatic Classification Plugin (SCP): Built by Luca Congedo, SCP provides a complete set of tools for processing and classifying multispectral satellite imagery. It supports downloading Landsat and Sentinel-2 data directly and running classification algorithms like Maximum Likelihood and Spectral Angle Mapping.