Geographic Unit Relationships
FEWS NET organizes annual sub-national data found in the Data Platform by the set of reporting units which existed at the time of collection, not to current reporting units. In order to maintain an accurate history of those units and the changes that have occurred over time, FEWS NET creates and maintains what it calls a Relationship Table for each country’s reporting history. This consists of a record of the names, identification codes, and relationships between the units for every year of data, creating a genealogy of reporting units for each country. This same information is used to create country-specific Annual Boundary Sets, listing each reporting unit that existed during a specific year.
Constructing Geographic Unit genealogy
The process starts for each country by preparing a list of the names and hierarchical relationships of all the sub-national reporting units that existed in a starting year. These may be administrative units or other types of geographic units developed specifically for a data type such as crop reporting units, Landscan population data, or markets and price data.
Each entity is assigned a unique FEWS NET identification code (a FEWS NET ID, or FNID) which also locates them in the national-level hierarchy of reporting units (Admin 1, Admin 2, etc).
A year-by-year accounting of changes that have occurred in any of the reporting units is developed and annually updated. Depending upon the type of change that occurs, the relationship table and annual boundary set in use may have to change too.
There are no reporting unit changes during a year: The existing annual boundary set is not changed. The Relationship Table indicates that the existing set is still being used for the subsequent year.
A reporting unit changes name only: The reporting unit retains its same FNID. The existing annual boundary set is not changed.
A reporting unit’s geographic shape or hierarchical relationship is changed (e.g., it is merged with another unit or demoted from Admin 1 to Admin 2): The FNID of the reporting unit is changed and a new annual boundary set must be created. This new annual boundary set becomes effective as of that year. Learn more about FEWS NET’s geographic unit relationship types.
When a new annual boundary unit set is created, the resulting genealogy of temporal and hierarchical relationships between all reporting units is entered into the FDW where it guides how statistical data are matched with the right boundaries.
A typical country in the FDW may have 2-5 annual boundary sets, depending upon how active it has been in changing its sub-national boundaries. Some countries, like India, have made changes every year to their line-up of reporting entities, and have one annual boundary set for each of the 40+ years of agricultural data.
Why FEWS NET uses this approach
This approach allows a user to accurately reconstruct the reporting units in use for any country at any point in time. This can provide valuable analytic context. When looking at historical crop production, for example, knowing when a reporting unit was split or merged provides an analyst with an understanding of when the unit’s hectarage and yield estimates may have drastically changed, not because of poor weather, but because the unit has become either larger or smaller due to a change in its shape/location/dimensions. This strategy allows a closer match between a variety of earth observation indicators and crop outcomes. It is especially important in detecting and objectively objectively measuring climate change impacts on yield, and building more accurate crop estimation techniques.
Notes on crop reporting units
FEWS NET organizes annual sub-national crop production data by the set of reporting units which existed at the time of the harvest. Often, these reporting units are also administrative units. But when a country’s crop data is not reported by administrative boundaries, then FEWS NET must create relationship tables and annual boundary sets which match those used by the country.
FEWS NET’s crop data relationship tables and annual boundary sets most often use a start date in the early 1980s because that’s when it became important to match crop reporting boundaries and statistics with newly emerging satellite-based observation data used for early warning of changes in a country’s food production capabilities.