Included also is a regression trend line that shows how value tends to vary with size. For example, 5 acre parcels will tend to sell for between $30,000 and $40,000 per acre, one acre parcels between $90,000 and $100,000, etc.
Of course, individual property values will vary depending upon location, access, vegetation, views, water/sewer, etc., demonstrated by the splayed dot pattern.