This code system http://hl7.org/fhir/measurereport-stratifier-value-example defines the following codes:

CodeDisplayDefinition
northwest NorthwestNorthwest region stratification.
northeast NortheastNortheast region stratification.
southwest SoutwestSoutwest region stratification.
southeast SoutheastSoutheast region stratification.
<status value="active"/><experimental value="true"/><publisher value="Clinical Quality Information Workgroup"/><description value="Example Region Value Measure Groups for the Measure Resource."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/measurereport-stratifier-value-example"/><content value="complete"/><concept><code value="northwest"/><display value="Northwest"/><definition value="Northwest region stratification."/></concept><concept><code value="northeast"/><display value="Northeast"/><definition value="Northeast region stratification."/></concept><concept><code value="southwest"/><display value="Soutwest"/><definition value="Soutwest region stratification."/></concept><concept><code value="southeast"/><display value="Southeast"/><definition value="Southeast region stratification."/></concept></CodeSystem>