A very easy way to visualize which entities were most often the target of a terrorist attack is via a wordcloud. The standard way of generating word clouds is using the python module wordcloud.
After cleaning the data to make it useful, a short python script gives the following output.
As one can see, regular citizens are most frequently the target of attacks. On the second place, all kinds of private instances are found. Afterwards, police officers and government officials are targeted.
The reason we chose for this visualization is for its simplicity, yet giving a lot of information in a glance.
Data Visualization Blog KU Leuven 