One FeatureCollection
GeoJSON output holds a single collection. When your GPX has more than one of the three groups — waypoints, routes and tracks — mapverter merges them into one FeatureCollection, gives each feature a layer property naming its group, and mentions the merge in the conversion report. A GPX with only tracks, for example, needs no merge and gets no layer property.
Geometry and elevation
Waypoints become Points. Routes and tracks become LineStrings, and a track with several segments becomes a MultiLineString. Elevation from <ele> stays as the third coordinate, and because GPX is already WGS 84, coordinates are written unchanged.
Properties
Values such as name, desc, time, sym and type become properties of each feature. The times recorded at each track point are not carried over, so a track keeps its shape but not the time of every point.