Sentence:  Let's say you get a new customer across town and you don't have any other customers over there. You still need to be competitive with price, but it costs too much money to send crews or a serviceman to one account across town. You need to get more customers over there for margins to exceed the costs of going over there. Once you hit a certain <WSD>density</WSD>, you're in the black. 
Meaning of the word marked with <WSD> tags:  (number of particles or other quantity contained by a given volume)The ratio of one quantity to another quantity.