Malcolm has done a wizard job of calculating the amount of track on an annual basis within a 40km radius of Holkham Hall in Norfolk. The graph is here:
The regression is a time-series, and so we have to remove the effects of auto-correlation over time. I've omitted all the subscripts for time for clarity. We can use ARIMA for the regression. This is exciting and a great way to spend the holiday! Thanks Malcolm for your speedy work. I'll be back with some statistical output shortly.