Local governance is the school for democracy. At the local level, individual voices, votes and actions can and do make a difference. A state legislature at any time can alter the boundaries of any local government, expand or narrow its power or completely abolish it all together.
Local governments are legally subordinate to the states - it is a unitary relationship.
The majority of voters living within the proposed city boundaries must approve incorporation. After the incorporation, the residents can draft a proposal to change from a general law to charter law city. Again, approval must done through the majority vote of the people. A general law city operates under certain general conditions as specified by the state. Cities that operate under general law have services delivered to them by the county, special districts and internally.