FEWS NET organizes sub-national data in the Data Platform using the reporting units in effect at the time of data collection.
In order to maintain an accurate history of the Geographic Units and the changes that have occurred over time, FEWS NET creates and maintains a relationship table for each country’s reporting history.
A relationship table provides a record of the names, identification codes, and relationships between the Geographic Units for every year of data, creating a genealogy for each country. This same information is used to create country-specific Geographic Unit Set Versions that specify the Geographic Units that existed during a given year. Relationship tables and Geographic Unit Set Versions allow data to be compared more effectively over time.
Development of Geographic Unit genealogy
Geographic Unit Set Versions contain a specific type of reporting units. For example, administrative units (such as a state, county, or province) or another type of Geographic Unit such as a crop production reporting region or market.
A year-by-year accounting of changes that have occurred in any of the reporting units is developed as follows:
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The names and hierarchical relationships are documented for a starting year.
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Each Geographic Unit is assigned a unique FEWS NET identification code (a FEWS NET ID, or FNID) which also locates them in the national-level hierarchy of Geographic Units (Admin 1, Admin 2, etc).
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The relationship table and annual boundary set in use may change depending on the type of reporting unit changes that occur:
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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.
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A reporting unit changes name only: The reporting unit retains its same FNID. The existing annual boundary set is not changed.
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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 Geographic Unit Set Version becomes effective as of the starting year. Learn more about FEWS NET’s Geographic Unit relationship types.
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When a new Geographic Unit Set Version is created, the resulting genealogy of temporal and hierarchical relationships between the Geographic Units is entered into the FEWS NET Data Warehouse (FDW) to match statistical data to the correct boundaries.
Frequency of Geographic Unit Set Version changes
A typical country in the FDW may have 2-5 Geographic Unit Set Versions for administrative or crop reporting units, depending on how actively a country has changed its sub-national boundaries.
For country-specific information on reporting units and changes over time, see the Country Data Books.
Using historical Geographic Units during analysis
The ability to accurately reconstruct the reporting units in use for a country at a given point in time provides valuable analytic context.
When looking at historical crop production, for example, a drastic change to a unit’s hectarage and yield estimates may be due to a change in the unit’s shape, location, or dimensions rather than weather conditions. Knowing when a reporting unit was split or merged allows a closer match between earth observation indicators and crop outcomes.
This approach is especially important for detecting and objectively measuring climate change impacts on yield, and building more accurate crop estimation techniques.
Accessing Geographic Unit relationships from the FEWS NET API
You can use the following endpoint to access Geographic Unit relationships defined in FDW: https://fdw.fews.net/api/geographicunitrelationship/. For example, pull Geographic Unit relationships for Kenya in JSON format using https://fdw.fews.net/api/geographicunitrelationship.json?country_code=KE. For more information about constructing API requests, see FEWS NET API.
Notes on crop reporting units
FEWS NET organizes annual sub-national crop production data using the set of reporting units that existed at the time of the harvest. Often, these reporting units are also administrative units. When a country’s crop data is not reported by administrative boundaries, FEWS NET creates relationship tables and Geographic Unit Set Versions which match the crop production reporting boundaries used by the country.
In the early 1980s, 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. As a result, many crop data relationship tables and Geographic Unit Set Versions have start dates from this period.