Consider equalEarth as default projection type

[jwoLondon]

Now that equalEarth is one of the core Vega projection types, would you consider making it the default projection type rather than mercator? Apart from its familiarity, I see little advantage in using the mercator projection for most cartographic data. It is particularly problematic for global maps that don't focus on high latitudes.

Equal Earth with its proportional area projection, horizontal lines of latitude, no extreme shape distortion and curved bounds only for oceanic areas provides a much more suitable default for the kinds of mapping to which Vega is suited.

I think there is also an argument for making the identity projection the default given this Is conceptually close to 'unprojected'. Although on balance, less desirable than equalEarth as it may cause backward compatibility problems without reflecting the y scale.

See also https://github.com/vega/vega-lite/issues/5367