pgRouting: Nodes vs. Source/Target

Question

I am working within a local city government on creating a routing network and started last week with little to no knowledge of pgRouting. I want the routing network to be used by our fire department and public schools. A series of travel-time buffers radiating from each fire-station is my goal. Example: how far can we travel in 1 min? 5min? 10min? from each station.

I found what visual I am looking for via:https://anitagraser.com/2011/02/12/drive-time-isochrones/

So far I have successfully created a database for the routing, created both extensions (PostGIS & pgRouting), imported my shapefile road centerlines successfully into my database, and lastly I ran pgr_createtopology. The results are great! My pgRouting plugin within QGIS works flawlessly. The next step is where I need help!

Should I create nodes? Or, alternatively, can I just use the vertices from the ""_vertices_pgr table generated from function: pgr_createTopology?

The ""_vertices_pgr table contains an "id" column but I can't see any column with any geographic data within the table. Is this why we can't use the vertices table? Is there something I am misunderstanding about creating a node network when I already have vertices created from pgr_createTopology?

Answer 1

For shortest path Dijkstra or driving distance queries you only need a valid network topology with source and target attributes in the network table.

The _vertices_pgr table is generated when you run pgr_createTopology function or when you use osm2pgrouting. It can be convenient later, for example when you want to link the node geometries with the result of your drivetime query. `

In case you want to recreate the vertices table, you can use pgr_createVerticesTable function.

The id column in the vertices table can be linked with the source and tatget coulmn of the network table.