PgRouting analyzes graphs to find the shortest path between two nodes through edges. In a street network, you can think of nodes as intersections and edges as the streets themselves. I will be using the Chicago street network, which can be found here. I have also uploaded it to the server, named chicagostreets.
1. In order to develop data capable of using PgRouting a source and target geometry must be set up at the start and end of each road. These will serve as the start and end destination points. To perform this follow the “Creating a routable road network” section of this tutorial (blog also has many helpful QGIS tutorials). Another thing to get familiar with in SQL is the WITH Clause. This allows you to reference other SQLs within one query.
2. Once your network is made you can start routing. Follow this tutorial to get multiple options for routing. pgr_dijkstra and pgr_kdijkstraPath are two that work well for visualizing one path or one startpoint to many paths.
3. By joining the geometries in your network to the results of your routing you can import this into QGIS and see your paths.
To reference my SQL query from the tutorial in class, click link.