The call of the variable isn't correct and it should look like:
Sum({<Year={$(vYear)}>} $(vTotalFootFall))
Beside this the last part of your variable contains a sum() and with it you tries to nest aggregations without setting them into an aggr() and further the closing bracket of the function is missing.
Another point you are using something like a + b + c. If any of the operands didn't contained a valid numeric value the whole result on this row-level will be NULL. If this isn't wanted you should use: rangesum(a,b,c).
Further it looked that your time-buckets are distributed within multiple fields. In the majority of the use-cases this has more disadvantages as benefits and so it could be more suitable to transform it into a stream-data structure.
- Marcus
