Mapping Tanzania: A QGIS Workflow for Temporal Analysis and Database Integration

Whether you are tracking urban expansion, environmental changes, or demographic shifts, QGIS is a powerhouse for visualizing spatial data. This tutorial will walk you through setting up a robust spatial workflow, from connecting your central database to preparing your layers for web publication.

Prerequisites

Before diving in, ensure you have the following ready:

• QGIS installed on your machine.

• Access to your PostgreSQL 17 database (with the PostGIS extension enabled).

• Your base shapefiles or raster datasets for Tanzania, specifically the historical data for 1995 and your projections or current data for 2025.

• Credentials for your GeoServer instance.

Step 1: Connecting QGIS to PostgreSQL 17

Centralizing your spatial data in a database rather than relying on local shapefiles ensures data integrity and easier collaboration.

1. Open QGIS and navigate to the Browser Panel on the left.

2. Right-click on PostgreSQL and select New Connection.

3. Fill in your connection details:

   • Name: Give it a recognizable name (e.g., Tanzania_Spatial_DB).

   • Host: Your database server's IP address or hostname.

   • Port: Default is usually 5432.

   • Database: The specific name of your PostGIS-enabled database.

4. Under the Authentication tab, enter your username and password.

5. Click Test Connection. Once successful, click OK. You can now drag and drop spatial tables directly from the Browser Panel into your map canvas.

Step 2: Loading and Visualizing Temporal Data (1995 vs. 2025)

To analyze changes over a 30-year period, we need to bring both datasets into the project and style them for clear comparison.

1. Load the Data: Drag your 1995 and 2025 datasets (either from your local files or the newly connected PostgreSQL database) into the Layers Panel.

2. Apply Thematic Styling:

   • Right-click the 1995 layer and select Properties > Symbology.

   • Choose a categorized or graduated color ramp that represents the baseline data clearly (e.g., a muted color palette).

   • Repeat the process for the 2025 layer, using a contrasting color palette or outline style to make the changes pop out.

3. Use the Swipe Tool (Optional): To visually compare the two years interactively, you can enable the "Map Swipe Tool" plugin (installable via Plugins > Manage and Install Plugins). This allows you to slide a bar across the screen to reveal the 1995 map underneath the 2025 map.

Step 3: Preparing Layers for GeoServer

Once your analysis is complete and your layers are styled, the next step is making them available on the web.

1. Ensure your layers are saved in a standard coordinate reference system (CRS). For national data in Tanzania, EPSG:4326 (WGS 84) or the appropriate UTM zone (e.g., EPSG:32736 for UTM Zone 36S) is highly recommended.

2. If you are serving the data directly from PostgreSQL, simply connect your GeoServer instance to the same database.

3. To replicate your QGIS styling on the web, right-click your styled layer in QGIS, go to Properties > Symbology, click the Style button at the bottom, and select Save Style > As SLD. You can upload this SLD file directly into GeoServer to maintain your exact visual design.