Time series using multiple datasets

Hello, 

I'm new to Power BI, so preemptive apologies if this request is lacking in necessary detail (or sense!) 

I am working with annual population data and would like to make a time series to show population change in working and non-working ages. However, I am getting stuck as each calendar year comes as a separate dataset. Is there a way to get Power BI to recognise that values from different datasets are related sequentially?

To make things more complicated, each calendar year's dataset comprises rows of small geographies (Area codes, below) that - when it comes to visualisations - I need to be able to aggregate into a range of larger geographies (i.e. to show population change for different area committees (second column), and for the whole region (all rows)). So I need to make sure any way of creating the sequence retains this geographical detail. 

I hope that makes sense. Any advice gratefully received 🙂