Although the main role of data visualization, in my opinion, is to make information easier to read and digest, many works have prioritized aesthetics before clarity.
Analysis of data, clustering, annotations, and layers is the role of datives, its a graphic designers job then to make it pretty.
Illustrations and shapes are used way more than photographs. although analysis of photographs and annotating/commenting directly on the image can present ideas we haven’t thought of before, its more real, and makes us more aware of the world around us as we start noticing things and probably analyze and visualize in our heads. -minority report style 
Data visualization is done through 3 main steps: 1- Data gathering 2- Data Analysis 3- Data visualization. The first step can done in two ways, starting off by gathering data and trying to see similarities/differences, or asking a question and collecting data to answer it.