Show projected data on maps

[sophiamersmann]

Core problem

• When dealing with projected data, authors usually include two indicators, one for historical data, one for future projections
• Line charts stitch them together, but maps do not (see screenshots below)

Example chart: https://ourworldindata.org/grapher/population-growth-rates

Proposed solution

Maps should combine past and future data, if both are available. Probably needs some design work: What visual cue are using to differentiate between past and future data?

[larsyencken]

It makes me wish for a different internal data model for projected data, like a pair of time series, one of values and one saying if it's a projection or not.

It's not clear what strategy would be good for indicating it. A shift in title? A different tooltip?

@danyx23 Perhaps whether or not a data point is projected would be a good hidden dimension for a dimensional indicator.