Exploring Hierarchies Using the DAGMap - Methods for Multilevel Analysis and Visualisation of Geographical Networks - page 105

Linked highlighting enables structures in the Sugiyama layout to be easily
identified at a glance. Consulting the Sugiyama layout orients the user in the DAG
because spatial position is used to encode the node position and the level in the
hierarchy. Simply drawing DAG edges on the treemap view obscures the level and
the position of the structure in the hierarchy.
Second, extracting a spanning tree biases an arbitrary subtree of the DAG,
randomly assigning the subtree more to one owner company than another owner
company. However, a subtree can only be chosen by using information obtained
from exploring and visualizing the datasets.
The DAGMap indeed lays out useful and complementary information on differ-
ent parts of the screen while linking corresponding cells through user interaction.
In a sense, unfolding the DAG along with our visualization system provides a
framework for exploring any hypothesis.

7.3 Case Study

Part of this work was completed in collaboration with geographers in the National
French Research Program SPANGEO 1 . Some data were obtained from the Orbis
database maintained by the Bureau van Dijk office 2 , and some of the data were man-
ually collected. The full dataset encompasses approximately 140,000 companies,
which emerge as subsidiaries of 597 main companies that cover numerous industrial
sectors. Companies (and subsidiaries) are linked to one another by approximately
250,000 links. However, geographers are not interested in studying the full dataset
but would rather focus on specific sectors of activity (NACE code). Alternatively, a
part of the DAG that corresponds to selected major companies (source nodes) can
be computed and explored separately. In this case study, we consider a DAG that
spans the subsidiaries of a major European car manufacturer.
The visualization helps geographers determine how companies follow territorial
logics or, in contrast, develop their activities based on other concerns. Strategies
differ from one group to another. For example, Peugeot's organization is completely
different from that of Renault. However, strategies also differ between sectors.
Food companies tend to sell their products locally. The car industry is organized
differently, producing parts in lower-cost countries, assembling the cars in another
country, and shipping the vehicles to wherever markets exist. The picture becomes
even more complex when companies expand their activities over several industrial
sectors. Typically, a company will develop subsidiaries in the financial sector
that manages financial flows generated by the overall activity of the company.
Consequently, commercial and financial strategies intertwine over several industrial
sectors.

1 See the URL s4.parisgeo.cnrs.fr/spangeo/spangeo.htm
2 See the URL www.bvdep.com/en/orbis.html