Below and above average query for a scatter plot

I have a scatter graph plotted in excel

On the x axis is distance from CBD and on the y axis is accessibility. I have given every station in a rail network an accessibility value and plotted this with how far away it is from the CBD. In total there are 103 stations which I grouped in the graph according to the different boroughs they are located in. I made a trend line for all the stations and now what I want to know is whether this means that stations below the trend line perform below average accessibility wise and vice versa. The purpose of this is to see whether boroughs as a whole have below or above average connectivity.

I have attached the graph
excel forum graph.xlsx

Your question probably goes beyond Excel, as the question would be the same whether you performed this analysis in Excel or any other way.

I'm no expert on public transportation (assuming this is a public rail network on not freight), so I can't claim any expertise in judging the correctness of your analysis. In general, a trendline does provide an "average" based on the information the trendline is based on. In your case, it is based solely on distance from CBD (I don't know what CBD stands for, but I'm guessing Central something or another). It neglects any other possible variable (such as population or ridership) that might impact accessibility.

In short, I believe a trendline based on these data could be used to indicate an average accessibility, and, by extension, which stations have above or below average accessibility based solely on distance from CBD. Whether there are other variables that still need to be considered depends on the overall scope of the project this is part of.