Currently, most of the parsing errors in geoparser.cpp assume the user already knows what the problem is. For example:
"GeoJSON coordinates must be an array of coordinates" (without saying what the actual erroneous type is)
"Point must only contain numeric elements" (without saying what the actual type of the provided element was)
"Coordinates of polygon must be an array" (etc)
"MultiPolygon coordinates must be an array"

In order to make problem diagnosis easier, we should provide as much context as possible in these error strings.