The term "West Michigan" seems like it should be relatively easy to define, yet it means different things to different people in different circumstances.
Approximate delineation of literal definition of "West Michigan"
West Michigan Tourist Association
The West Michigan Tourist Association shows a map of West Michigan that is very much the same as this literal definition. It further subdivides West Michigan into "Northern West Michigan," "Central West Michigan," and "Southern West Michigan."
Approximate delineation of "Southwest Michigan"
West Central Michigan
West Central Michigan is perhaps the closest to the locally understood definition of "West Michigan". It can be thought of as Grand Rapids, Muskegon, Grand Haven, Holland, and the surrounding area. This aligns well with the 1999 Grand Rapids-Muskegon-Holland Metropolitan Statistical Area (MSA), which included Allegan, Kent, Muskegon, and Ottawa Counties.
Approximate delineation of "West Central Michigan"
Redefining Statistical Areas
In 2005, the Metropolitan Statistical Areas were redefined. Grand Rapids is now a part of the Grand Rapids-Wyoming MSA, which includes Barry, Ionia, Kent, and Newaygo Counties. Muskegon and Ottawa Counties both have their own individual MSAs called the Muskegon and Holland-Grand Haven MSAs, respectively. Allegan County is now considered an individual Micropolitan Statistical Area. Together these counties form the Grand Rapids-Muskegon-Holland Combined Statistical Area (CSA). Given commuting patterns, urban sprawl, and regional collaboration, the CSA is perhaps the best way to consider "West Michigan" in the near future.
Approximate delineation of the Grand Rapids-Muskegon-Holland Combined Statistical Area
Many atheletic teams have been named under the psychographic assumption that if the team is named for a larger region, it will draw a larger fanbase. This may be the reason that the Comstock Park-based minor league baseball team is named the West Michigan Whitecaps.