Where one choropleth layer came from: the polygon series amCharts drew, and
the field names a declaration renamed its facts to, when the author gave
one.
The fields have to travel with the series because they change which
regions the layer kept: a map whose value hangs on a column amCharts was
never bound to reads as no regions at all without them, and the highlight
would then index a list of a different length from the one the reader is
walking.
Where one choropleth layer came from: the polygon series amCharts drew, and the field names a declaration renamed its facts to, when the author gave one.
The fields have to travel with the series because they change which regions the layer kept: a map whose value hangs on a column amCharts was never bound to reads as no regions at all without them, and the highlight would then index a list of a different length from the one the reader is walking.