I don't think the graph is supposed to be particularly useful to you, I think this graph is more useful to the actual city workers so they can focus on specific

I don't think the graph is supposed to be particularly useful to you, I think this graph is more useful to the actual city workers so they can focus on specific complaints at specific times. There's no point focusing on streetlight complaints at 6pm, and there's no point focusing on noise at 7am when the garbage trucks are going around. Deal with the right problems at the right time gets a much better response from your customers (IE the tax payers and voters). In general you want to deal with the vast majority of complaints. The rising and falling of the line is caused by something else becoming larger. You don't follow the line itself, but judge its thickness by placement on the X-axis.