The ERS Commuting Zones (CZs) and Labor Market Areas (LMAs) were first developed in the 1980s as ways to better delineate local economies. County boundaries are not always adequate confines for a local economy and often reflect political boundaries rather than an area's local economy. CZs and LMAs are geographic units of analysis intended to more closely reflect the local economy where people live and work. Beginning in 1980 and continuing through 2000, hierarchical cluster analysis was used along with the Census Bureau's journey to work data to group counties into these areas. In 2000, there were 709 CZs delineated for the U.S., 741 in 1990, and 768 in 1980. LMAs are similar to CZs except that they had to have a minimum population of 100,000 persons. LMAs were only estimated in 1980 and 1990. This was done in order for the Census Bureau to create microdata samples using decennial census data (1980 PUMS-D, 1990 PUMS-L) that avoided disclosure. The LMAs were discontinued in 2000 because researchers found them to be too large and not as useful as the CZs. The identical methodology was used to develop CZs for all three decades.