QGIS: Basic Tutorial for Government Geospatial Projects

QGIS is the most widely used open-source geographic information system in the world. For government entities in Colombia, it represents a robust, license-free alternative to commercial solutions. This guide is designed for government staff who need to work with geospatial data but do not have specialized GIS training.

What is QGIS and why it matters to your organization

QGIS is software that allows you to visualize, edit, analyze, and publish geographic information. In the context of a municipality or regional environmental authority, this translates to:

• Visualizing your municipality's properties over updated orthoimagery.
• Analyzing public service coverage by zone.
• Identifying risk areas by crossing hazard layers with land-use layers.
• Generating thematic maps for development plans and land-use plans (POT).

The main advantage: it is completely free, has constant updates, and is backed by a global community.

Installation

Windows

1. Download QGIS from qgis.org/download.
2. Choose the LTR (Long Term Release) version — it is the most stable and recommended for production environments.
3. Run the installer. The standard installation includes everything you need.

Recommendations

• Install the 64-bit version if your system supports it.
• You do not need to install additional plugins to get started. Plugins are added later as needed.
• The current LTR version (3.34) is excellent for institutional work.

First steps: loading data

Shapefiles

The Shapefile format (.shp) remains the most common format in Colombian government geospatial data. To load one:

1. Menu Layer > Add Layer > Add Vector Layer.
2. Select the .shp file. Ensure the companion files (.dbf, .shx, .prj) are in the same folder.
3. Verify the coordinate system. In Colombia this will generally be MAGNA-SIRGAS / Colombia Bogota (EPSG:3116) or one of the zones in the official projection system.

GeoJSON files

GeoJSON is a modern JSON-based format that is easier to share and does not require multiple files:

1. Menu Layer > Add Layer > Add Vector Layer.
2. Select the .geojson file.
3. QGIS will automatically detect the coordinate system (generally WGS 84).

Raster files (orthoimages, DTM)

To load orthoimages or digital terrain models:

1. Menu Layer > Add Layer > Add Raster Layer.
2. Select the file (.tif, .ecw, .jp2).
3. For large files, QGIS will automatically generate pyramids to improve display performance.

Visualization and symbology

Changing layer style

1. Double-click the layer in the layers panel > Symbology tab.
2. Choose the representation type:
   • Single Symbol: All features with the same color.
   • Categorized: A different color per category (example: land-use type).
   • Graduated: Colors that vary by a numeric value (example: property area).

Labels

To display names or identifiers on features:

1. Double-click the layer > Labels tab.
2. Select Single Labels.
3. Choose the field to display (example: property_name or cadastral_number).

Basic spatial queries

Selection by attributes

To find specific properties by their cadastral number or owner:

1. Menu Edit > Select > Select by Expression.
2. Write the expression. Example: "terrain_area" > 5000 will select all properties with area greater than 5,000 m².

Selection by location

To find which properties are within a specific zone:

1. Menu Vector > Research Tools > Select by Location.
2. Choose the input layer (properties) and the selection layer (area of interest).
3. Select the spatial relationship type: Intersects, Within, Contains.

Buffer

To create influence zones around features:

1. Menu Vector > Geoprocessing Tools > Buffer.
2. Define the distance. Example: a 30-meter buffer around rivers to identify riparian zones.

Connecting to PostGIS

PostGIS is the spatial extension of PostgreSQL and is the database we recommend for institutional geospatial management. QGIS connects natively:

1. Browser panel > right-click PostGIS > New Connection.
2. Enter connection details: server, port (5432), database, username, and password.
3. Once connected, you can drag tables directly onto the map.

The advantage of PostGIS over local files is that multiple users can work on the same data simultaneously, with version control and permissions.

Publishing with GeoServer

GeoServer allows you to publish your layers as web services (WMS, WFS) that other systems can consume. The basic workflow:

1. Store your data in PostGIS — GeoServer connects directly to the database.
2. Configure GeoServer to publish layers as WMS services (for visualization) or WFS (for download).
3. Consume the services from QGIS, web applications, or any OGC-compatible system.

At GEOSAT we use this architecture (PostGIS + GeoServer + QGIS) as the foundation for our spatial data infrastructure projects for government entities. It is the same stack that powers Terraes, our cadastral platform.

Additional resources

• Official documentation: docs.qgis.org — available in multiple languages.
• Recommended plugins: QuickMapServices (for loading base maps like Google Satellite or OpenStreetMap), qgis2web (for exporting interactive web maps).
• Colombia open data: datos.gov.co and the IGAC portal for cadastral and cartographic data.

Next step

QGIS is the gateway to the geospatial world for any government entity. Once your team masters the basic operations of loading, visualizing, and querying data, the natural next step is implementing a spatial data infrastructure with PostGIS and GeoServer that centralizes municipal information.

If you need support implementing a municipal SDI or training your team on geospatial tools, at GEOSAT we offer consulting and training services adapted to your organization's technical level.