Evaluation Results
We were able to identify 246 unique users that are sharing
incident related tweets. Using the description of the users’
Twitter profile, we manually labeled all users with different
categories. Following the approach described in Choudhury
et al. (2012) we identified five user categories. Official
organizations like the Seattle Fire Department are categorized
as emergency management organizations (EMO). Organizations
not related to emergencies, like magazines, are
clustered as other organizations (ORG). Furthermore, we
found specialized traffic reporters or journalists, which are
represented as journalists/bloggers focused on emergency
management (EMJ), in contrast to other journalists/bloggers
(JOU). Citizens are categorized as individual users (I).
The first bar of each stacked cluster in Figure 1 shows
the distribution of the number of users for each category according
to the different types of incidents. We can notice
that a variety of different individual users (196) are reporting
about the three incident types. On the other side, only
few emergency management organizations (11) and focused
journalists (2) are publishing incident related microblogs.