A Graph for Every Problem - Graph Analysis and Visualization - page 56

Figure 2-18: An Aperture JS link rose diagram summarizes flow in each
direction around a node. Here, flow of commodities to other states is
shown using 1997 Commodity Flow Survey data from the U.S. Department
of Transportation's Bureau of Transportation Statistics.
However, when the goal is to show traffic along routes, as shown in Figure
2-17 , and a large number of them exist, you can subdivide the spatial field
recursively into tiles and aggregate by tile cell for better scalability. Figure
2-19 shows a tile-based visualization of shipping traffic statistics. Areas of
high traffic in this graph (such as the capes of South Africa and the coast
of Japan) appear in red and black. Chapter 14 provides more examples of
tile-based approaches.
Figure 2-19: You can use tile-based aggregation and rendering techniques
to graph a very large number of links, as in this visualization of shipping
traffic over a period of a year.
Note
Chapter 13, “Spatial Networks,” provides more in-depth information on
visualization and analysis of spatial networks.