Your questions will produce a very strong response bias by * sorting answers * preselecting answers * recommending answers * hiding other answers * restricting answers to different types of green * showing green area on OSM map

The example on the initial page would probably be classified as “landuse=residential” by most mappers.

You should distinguish between “surface=grass” and “landuse=grass” and offer both. On a “green” car park “surface=grass” is correct while “landuse=grass” is wrong.