On the line graph below, I've labelled the two main points or general trends that I'll describe in my overview. Look at the big red numbers 1 and 2.
Point 1 refers to the years when all three lines were at their highest points. Point 2 refers to the line for "business visitors", who appear to have spent the most overall.
So here's my overview paragraph:
It is noticeable that overall spending by international visitors to New Zealand was at its highest between the years 2000 and 2003. Also, over the 20-year period shown, business travellers spent the most per day, on average, while people visiting friends or relatives spent the least.