The blog post explores the implementation of a two-level Sankey graph to visualize network traffic patterns using Vega in Kibana 6.2. A Sankey diagram, which illustrates the flow quantity between nodes with varying line widths, is created using Elasticsearch and Kibana, along with sample data generated by the makelogs utility. The visualization allows users to view all traffic or filter it by selecting specific source or destination countries. The post outlines the process of setting up the environment, generating data, and crafting the visualization using various data tables and transforms in Vega, such as nodes, edges, and groups. It emphasizes user interactions through signals for dynamic filtering and highlights debugging strategies using browser tools. The post also provides insights into manipulating Vega code to customize the graph's appearance and interactions, offering a detailed walkthrough of the technical steps involved in creating this visualization.