Using a client-side webmapping library (openlayers3 or leaflet), I want my user to be able to add one marker on the map. I will then be able to retrieve long/lat coordinates.
From that, I want to know if it is located inside a polygon (from another layer) and retrieve polygon attributes. Is that possible ?
Yes that's possible. With leafletjs you can use this Mapbox API: leaflet-pip
Once you have captured the users clicked coordinates you can use them like in the example linked above:
var userCoords = ????
var gjLayer = L.geoJson(statesData);
var results = leafletPip.pointInLayer(userCoords, gjLayer);
This will give you an array of polygons that contain that point, along with all the polygons attributes.
