• A one-dimensional variable with the same name as a dimension and that specifies coordinate values for dimension is a coordinate variable, for example the variables lat, lon, pres, and time in this example from the CF conventions:

    dimensions:
      lat = 180 ;
      lon = 360 ;
      pres = 15 ;
      time = unlimited ;
    variables:
      float xwind(time, pres, lat, lon) ;
        xwind:long_name = "zonal wind" ;
        xwind:units = "m/s" ;
      float lon(lon) ;
        lon:long_name = "longitude" ;
        lon:units = "degrees_east" ;
      float lat(lat) ;
        lat:long_name = "latitude" ;
        lat:units = "degrees_north" ;
      float pres(pres) ;
        pres:long_name = "pressure" ;
        pres:units = "hPa" ;
      double time(time) ;
        time:long_name = "time" ;
        time:units = "days since 2000-1-1 0:0:0" ;
    

  xwind(n,k,j,i) is associated with the coordinate values lon(i), lat(j), pres(k), and time(n).

• A two-dimensional variable of type char is a string-valued coordinate variable if it has the same name as its first dimension, for example:

    dimensions:
       month = 12;
       abbrev_len = 3;
    variables:
       month(month, abbrev_len);
    data:
       month="jan", "feb", "mar", ..., "dec";
    

• Multidimensional auxiliary coordinate variablesa, identified by a coordinates attribute, may be needed for projections, as in this example from the CF conventions

   dimensions:
     xc = 128 ;
     yc = 64 ;
     lev = 18 ;
   variables:
     float T(lev,yc,xc) ;
       T:long_name = "temperature" ;
       T:units = "K" ;
       T:coordinates = "lon lat" ;
     float xc(xc) ;
       xc:axis="X";
       xc:long_name = "x-coordinate in Cartesian system" ;
       xc:units = "m" ;
     float yc(yc) ;
       yc:axis="Y";
       yc:long_name = "y-coordinate in Cartesian system" ;
       yc:units = "m" ;
     float lev(lev) ;
       lev:long_name = "pressure level" ;
       lev:units = "hPa" ;
     float lon(yc,xc) ;
       lon:long_name = "longitude" ;
       lon:units = "degrees_east" ;
     float lat(yc,xc) ;
       lat:long_name = "latitude" ;
       lat:units = "degrees_north" ;
    

• Make coordinate variables for every dimension possible (except for string length dimensions).
• Give each coordinate variable at least unit and long_name attributes to document its meaning.
• Use an existing netCDF Convention, preferably CF if applicable, for identifying your coordinate variables.
• Use shared dimensions to indicate that two variables use the same coordinates along that dimension. If two variable's dimensions are not related, create separate dimensions for them, even if they happen to have the same length.
• For search and discovery metadata, add global attributes that specify bounding boxes, time ranges, and keywords, as recommended in NetCDF Attribute Convention for Dataset Discovery.

2007 Unidata NetCDF Workshop for Developers and Data Providers > Best Practices