Clarification of use of standard region names in "region" variables.
|Reported by:||martin.juckes||Owned by:||cf-conventions@…|
Description (last modified by martin.juckes)
The CF standard name region has the current description "A variable with the standard name of region contains strings which indicate geographical regions. These strings must be chosen from the standard region list." This description implies that the variable should be of character type, but it is often more convenient to have an integer variable and make a clear link to the region names using flag_values and flag_meanings. The proposal is to clarify the definition so that either usage is acceptable and include an example of the latter usage in the convention text. It is also proposed that an appendix be added to the CF Convention text to state clearly any constraints on file meta-data which are implied by the CF Standard Name definitions, so that it is possible to test such constraints in the CF checker.
New descriptions for CF standard names
A variable with the standard_name of region contains either strings which indicate a geographical region or flags which can be translated to strings using flag_values and flag_meanings attributes. These strings are standardised. Values must be taken from the CF standard region list.
A variable with the standard_name of area_type contains either strings which indicate the nature of the surface e.g. land, sea, sea_ice, or flags which can be translated to strings using flag_values and flag_meanings attributes. These strings are standardised. Values must be taken from the area_type table.
New usage example in CF Convention text
The following should be placed after example 3.3, renumbering examples 3.4 and 3.5 to 3.5 and 3.6 respectively (text checked for cross-references to "3.4" and "3.5" and none found)
A variable with standard name of region, area_type or any other standard name which requires string-valued values from a defined list may use flags together with flag_values and flag_meanings attributes to record the translation to the string values. The following example illustrates this using integer flag values for a variable with standard name region and flag_values selected from the standardized region names (see section 6.1.1):
Example 3.4. Flag variable with controlled values, using flag_values
int basin(lat, lon); standard_name: region; flag_values: 1, 2, 3; flag_meanings:"atlantic_arctic_ocean indo_pacific_ocean global_ocean"; ...... values:: basin: 1, 1, 1, 1, 2, .....
Hook in section 3.3 to highlight existence of constraints implied by standard name
In section 3.3, append to the paragraph about "description", after "The description is meant to clarify the qualifiers of the fundamental quantities such as which surface a quantity is defined on or what the flux sign conventions are. We don"t attempt to provide precise definitions of fundumental physical quantities (e.g., temperature) which may be found in the literature." the following:
The description may define rules on the variable type, attributes and coordinates which must be complied with by any variable carrying that standard name (such as in example 3.4).
Note that also that there is a typo in the text cited aboove don"t instead of don't