The first graph shows the BLS chemical plant operator employment data by state. Red represents the state (Texas) with the highest number of chemical plant operators (6,820 operators; as of 2012; based on BLS surveys). The graph shows in the lower left corner what the states’ colors indicate; from light green to dark green to blue to red signifying increasing numbers of chemical plant operators (and presumably numbers of chemical plants). Based on the data used for the graph, Texas has the higher number, followed by Louisiana, South Carolina, and Ohio. BLS reports no data for the states in white.
The second graph shows a somewhat different picture. On the graph, states are colored by the number of chemical plant operators per state’s square mileage. Note that whereas New Jersey and Massachusetts do not show high numbers of operators on the first graph, the second graph shows a high concentration of chemical plant operators (and presumably chemical plants) per square mile in these states. Absolute numbers (number of employed plant operators) versus concentration numbers (density; rate) for other states are also different, e.g. Texas and California. Data used to generate the second graph show that New Jersey has the highest density of operators (and presumably plants) followed by Louisiana, South Carolina, and Ohio.
Having relative comparisons of chemical plant operator concentrations (reflecting chemical plant density) seems to me to be a useful metric, perhaps more useful than the absolute numbers of operators and plants. Such a metric could be of value to chemical companies seeking a site for a chemical plant. Selecting a state with a high concentration (rather than only a high absolute number) might be advantageous. For example, finding chemical operators to employ might be easier in high concentration states and high concentrations indicate clusters and clusters are known to lead to competitive advantages.