As I understand, you already have the Dashboard element done, and just want to know how to navigate on to the Line chart.
Attached workbook simulates your data with a Filter Action on the main dashboard. This acts on Single Select of the State and City population text fields, to navigate to the Line chart.
Please mark answered if this addresses your question.
20180926 Canada cities_v10.4.twbx 117.3 KB
Thanks for your time. I have gone through the attached .twbx file.
In the below screenshot (red highlighted area), if you see there are two other Sheets, which have its own filters for City.
So in the Line Graph, two different trend lines for these two user entered cities should also appear.
Please advise on this.