Wash. Rev. Code § 36.93.010
The legislature finds that in metropolitan areas of this state, experiencing heavy population growth, increased problems arise from rapid proliferation of municipalities and haphazard extension of and competition to extend municipal boundaries. These problems affect adversely the quality and quantity and cost of municipal services furnished, the financial integrity of certain municipalities, the consistency of local regulations, and many other incidents of local government. Further, the competition among municipalities for unincorporated territory and the disorganizing effect thereof on land use, the preservation of property values and the desired objective of a consistent comprehensive land use plan for populated areas, makes it appropriate that the legislature provide a method of guiding and controlling the creation and growth of municipalities in metropolitan areas so that such problems may be avoided and that residents and businesses in those areas may rely on the logical growth of local government affecting them.
RCW 36.93.010