What is the difference between harmonized and year-specific geographic levels?
Harmonized geographic levels contain units with boundaries that are consistent over a specific time period. With these units, a researcher can complete a spatio-temporal analysis within the given time period without the complications of shifting boundaries. Harmonization is done by aggregating units that split or exchange land during the given time period, so that each unit represents the smallest possible consistent temporal footprint. View an example of harmonization here (insert picture).
If a researcher is not interested in examining multiple time steps, year specific units are available. A year-specific geographic level captures geographic units as they were for a particular survey or census, with the exception that some units may be combined for confidentiality purposes (see ). Both year-specific geographic levels and harmonized geographic levels (where applicable) are available for use with microdata and area-level data.