When the small municipality is part of a larger metro area, those commuters and out-of-town shoppers come from a large area and pass through this small administrational area, so it is natural that the ratio of things like arrest warrants can be large when compared to number of residents.
To understand this outside the context of Ferguson and the racially loaded atmosphere in this discussion, take for an example the City of London Police.
It's a police force that handles an area which has just 7400 residents. (Yes, that's the resident population in City of London). The police force for this area has 1300 employees, 750 of them full-time police officers. Are we saying that the ratio of policemen to residents is a sign of a horrible police state in London, with every tenth person in the city a police officer? No, of course not. There's a huge amount of crime? Well, many think so.
The ratio is so silly precisely because we're looking at a small area that belongs to a greater metropolis.