complete drawing
https://github.com/tomchentw/react-google-maps/issues/796

click-me popup
http://google-map-react.github.io/google-map-react/map/events

react leaflet
https://react-leaflet.js.org/en/

adding marker
https://stackoverflow.com/questions/41405343/adding-marker-to-google-maps-in-google-map-react

medium article
https://medium.com/front-end-hacking/simplified-google-maps-api-in-a-react-app-46981441d2c9

medium source
https://github.com/mthorry/simple-react-maps/tree/master/src

limit to 1 annotation / polygon
https://stackoverflow.com/questions/14166546/google-maps-drawing-manager-limit-to-1-polygon