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Electrical motors are fed via cables.  Both of these generate heat that is 
effectively energy lost, which costs money.  For a given mechanical load, the 
the voltage at the motor terminals and the motor efficiency determine the amount 
of electrical current that flows in the cable.  The current in the cable causes 
a voltage drop in the cable, affecting the voltage at the motor terminals, which 
in turn affects the current in the cable.  

A cable with a bigger cross-sectional-area reduces the cable resistance and 
voltage drop, which reduces energy loss, saving money in operation - but costs 
more in capital expense up front.  Bigger motors are more efficient but also 
cost more.  To optimize this we compare the annual cost of capital interest 
payments with annual cost of energy loss.  These first three vertical charts, on 
the left, are for different size cables.  The three on the right are the same 
for different size motors.

The heatmap is effectively the combination of the Cable and Motor "Cost Benefit" 
charts at the bottom.  The heatmap has "Cable Size" (cross-section in mm2) on 
the x-axis and "Motor Size" (rated Power in kiloWatts) on the y-axis.  The green 
colouring shows the cost optimum combination of cable and motor sizes - mostly 
affected by cable size.
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cheers -ben