Thanks Keith. All very good points. If you don't mind, where did you get your timezone polygons from? And what did you have to fix to get proper GeoJSON polys from those sources? One good source of data seems to be [Natural Earth Vector on GitHub](https://github.com/nvkelso/natural-earth-vector/tree/master/110m_physical), but the data comes in ShapeFile (.shp, .shx) and .DBF and .CPG formats, not something GeoPoly can use as-is :(