Please see my attached sample. Please consider the scatter chart which represents relation between population and NumberOfParks over the years for a particular city (Please make sure a city is always selected). I have represented NumberOfParks at Y=1 in the form of bubbles. There are two issues now:
1) Right now the size of bubbles represent the value of NumberOfParks at a particular Year. Instead it should represent how many times NumberOfParks has exceeded (or equal) a threshold (2 in this case) till this Year. For example, For City A, bubble for Year 2001 should be of size 1. For 2002, it should be 2, because this would be the second time observation for NumberOfParks to have crossed threshold.
2) Similar to NumberOfParks case represented at Y=1, Life Expectancy case should be represented at Y=2. It should again be in the form of bubbles with size depending on threshold (78 in this case).
Note: !Separate colored representation for Years is not compulsory.
