presto-orc/src/main/java/io/prestosql/orc/metadata/OrcType.java/OrcType/createOrcMapType
class OrcType:    private static List<OrcType> createOrcMapType(int nextFieldTypeIndex, Type keyType, Type valueType)
    {
        nextFieldTypeIndex++;
        List<OrcType> keyTypes = toOrcType(nextFieldTypeIndex, keyType);
        List<OrcType> valueTypes = toOrcType(nextFieldTypeIndex + keyTypes.size(), valueType);

        List<OrcType> orcTypes = new ArrayList<>();
        orcTypes.add(new OrcType(
                OrcTypeKind.MAP,
                ImmutableList.of(new OrcColumnId(nextFieldTypeIndex), new OrcColumnId(nextFieldTypeIndex + keyTypes.size())),
                ImmutableList.of("key", "value")));
        orcTypes.addAll(keyTypes);
        orcTypes.addAll(valueTypes);
        return orcTypes;
    }