Working with QGIS¶
Editing an AequilibraE network is editing any other node and link layer in QGIS. Before doing so, however, take a look at the discussion of the network triggers behind the AequilibraE network, particularly the section on network consistency behavior
Snapping to node¶
Before editing any transportation network, especially an AequilibraE network, one should enable the option to snap-to-vertex inside QGIS. This option will prevent the user from creating nodes that are infinitesimally close, yet disjoint. To enable this function, one can access the option Project > Snapping Options, click the little horseshoe, and then the Snapping on Intersection button, as depicted below
To make this option default for all future projects, one can access the menu Settings > Options and select the Digitizing menu from the side options. After that it is just a matter of enabling snapping by default, as shown below
In both cases you can tune how close you can (or have to) get to an existing vertex before the cursor snaps to it, but that is a purely preference issue.
From the QGIS manual “The option Enable topological editing is for editing and maintaining common boundaries in features mosaics. QGIS ‘detects’ shared boundary by the features, so you only have to move a common vertex/segment once, and QGIS will take care of updating the neighboring features.”
So if you are editing zoning layers, I highly recommend you go to the QGIS manual and read about it!
There are some basic tools in QGIS that might come in handy when you are working with AequilibraE, so we have described a few of them here.
In GIS, geometries can be SinglePart or MultiPart, where the first is what one would consider a regular geometry, while the latter is not always intuitive.
Examples of MultiPart geometries are countries that contain islands, so a geometry of the country should be formed of disjoint areas, or streets that are interrupted by the existence of a park. These elements, however, do not have place in traditional transport modeling, and we present a procedure to eliminate the occurrence below.
One can transform all MultiPart features into SinglePart ones using a QGIS standard tool, which can be accessed on Vector > Geometry Tools > Multipart to Singleparts.
Running it looks like this:
Just notice that, after this process to a network, you will HAVE to run through all the steps described in Preparing a network.
In order to add centroids to a network, one must first curate a layer of centroids and number them appropriately, as discussed in Adding centroids
QGIS has straightforward tools to extract centroids from areas, which can be accessed through the menu Vector > Geometry Tools > Centroids, as shown below
One should always remember to visually inspect the results of the automatic process, in this case looking for those centroids that were placed in awkward places and move them to more appropriate positions.
One might need to convert the zoning system to a SingleParts layer before following the instructions above, which can be done following the description provided in multipart_to_singlepart.