FEWS NET organizes annual sub-national data by the set of reporting units which existed at the time of collection, not to current reporting units. In order to maintain a link with the exact coordinates/locations of previous data, FEWS NET maintains relationship tables of geographic units.

To maintain the relationship tables, each of these reporting unit sets requires the preparation and maintenance of basic information about the set of reporting units which existed for each year. The record of the names, identification codes, and relationships between the units creates a genealogy of reporting units in each country. This information also informs FEWS NET’s country-specific annual boundary sets.

Constructing Geographic Unit genealogy

1. The process starts in each country by preparing a list of the names and hierarchical relationships of all the sub-national reporting units. 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 individual markets.

2. 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). 

3. A year-by-year accounting of changes that have occurred in any of the reporting units is developed.

   1. 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.

   2. A reporting unit changes name only: The reporting unit retains its same FNID. The existing annual boundary set is not changed.

   3. 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.

4. When a new annual reporting unit set is created, the resulting genealogy of temporal and hierarchical relationships between all reporting units is entered into the FDW.

A typical country, depending upon how active it has been in changing its sub-national boundaries, may have 2-5 annual boundary sets. Some countries, like India, have made changes every year to their line-up of reporting entities, and have one annual set for each year of agricultural data.

Why FEWS NET uses this approach

This approach allows a user to accurately reconstruct the reporting history of any reporting unit at any point in time. This can provide valuable context. When looking at historical crop production, for example, this will allow an understanding of when the unit’s hectarage and yield estimates may be expected to change simply because the unit has become either larger or smaller due to a change in its shape/location/dimensions. This strategy allows a close alignment between earth observations and crop outcomes, and an ability to objectively measure climate change impacts on yield, as well as build more accurate crop estimation variables.

Notes on crop reporting units

FEWS NET organizes annual sub-national crop 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 reporting does not use the exact same administrative boundaries, then FEWS NET creates a set of Crop Reporting Units.

Crop and climate data use a starting date in the 1980s because satellite imagery used in early warning began in 1982.