message: MINOR: Restrict the type of the exported symbol sphereProjection.
  To correctly incapsulate the projection APIs, the symbol
  `sphereProjection` should be exported as type `Projection` and not as
  `SphereProjection`.
diff: @@ -378,4 +378,4 @@ class SphereProjection extends Projection {
  }
  }
  -export const sphereProjection = new SphereProjection();
  +export const sphereProjection: Projection = new SphereProjection();
  