City planning focuses on the land use plans, spatial growth and policies which are at local level (affecting that particular city or town), whereas in case of regional planning the emphasis on the policies is more. Those policies become the guidelines for the urban areas and their existing plans are modified accordingly. This helps in meeting the larger requirement of the whole region.
Regional planning is an urban planning strategy that focuses on the social, economic, and environmental development of a specific area. Regional plans address the needs of the entire region rather than just one municipality. Regional planning is something you should consider when doing urban planning. The benefits of regional planning include coordination of transportation, housing, and other public services such as police, fire departments, hospitals, and schools.
Additionally, regional plans cover more of national level policies and issues & strengthens integrated development. City planning looks as a limited area when compared to a regional plan. Regional plan covers rural areas and undeveloped areas too which are usually not covered in town plans.
The categories, chapters, topics and aspects covered in both plans also differs because of the different needs and the existing developments. Village area, forests, undeveloped land and waste land might be completely missing from a city plan whereas it forms an important part of a regional plan.