See geotrellis.spark.filter.ToSpatial to get explanations about Metadata (M[K]) constrains
This exists because reduceByKey needs K and V to be members of
the ClassTag type class, but adding that restriction to the type
parameters of the class above would break the API.
This exists because
reduceByKeyneeds K and V to be members of theClassTagtype class, but adding that restriction to the type parameters of the class above would break the API. Neither method can be namedtoSpatialas that would hide the methods provided by the class above.