OpenStreetMap data for topology

A topological network, which specifies the formal relationships between geometric objects, requires real geographic data for it to be useful in an actual physical space. So next, we will acquire some geographic data in order to construct a network providing the shortest path between points in a physical space, following certain rules embedded in the network. A great source of data for this, and many other purposes, is OpenStreetMap.

Downloading the OSM data

Now, let's move back to QGIS to acquire the OpenStreetMap data from which we will create a topological network:

1. Navigate to Vector | OpenStreetMap | Download Data.
2. Select the newark_boundaries file as the From layer extent.
3. Enter c4/data/output/newark_osm.osm as the Output file and click on OK, as shown in the following screenshot:
   

Adding the data to the map

The downloaded data must be added to the QGIS project to verify that it has been downloaded and to further work on the data from within QGIS. Perform...