Rename _geoJsonStyle -> _style
Adds hover effect on the map features
Add tooltips
Only textual fields can be labels
Refactor variable name

"There are only two hard things in Computer Science: cache invalidation and
naming things" (Phil Karlton)
Use single quotes strings in JavaScript
Refactor a bit by caching this.options in a local variable
Set sizex and sizey to make it compatible with the dashboard