Organizing data by a named property such as region:

group USA {

  group Colorado {
    dimensions: time = unlimited, stations = 47;
    variables: float temperature(time, stations);
  }
  group Wyoming{
    dimensions: time = unlimited, stations = 61;
    variables: float temperature(time, stations);
  }
  group Alaska {
    dimensions: time = unlimited, stations = 53;
    variables: float temperature(time, stations);
  } 
  ...
  dimensions: time = unlimited;
  variables: float average_temperature(time);
}

• Like directories in a file system, Groups provide name spaces and a hierarchy of containers
• A Group is analogous to a netCDF-3 file: it may have variables, dimensions, attributes, types, and subgroups
• Use of Groups is optional, with backward compatibility maintained by putting everything in the top-level unnamed Group.
• Unlike HDF5, netCDF-4 requires that Groups form a strict hierarchy.

Potential uses for Groups include

• Factoring out common information
  • Containers for data within regions, ensembles
  • Model metadata
• Organizing a large number of variables
• Providing name spaces for multiple uses of same names for dimensions, variables, attributes
• Modeling large hierarchies

2009 Unidata NetCDF Workshop for Developers and Data Providers > Introduction to NetCDF-4