What are the essential principles or requisites for segmentation to be effective?

What are the essential principles or requisites for segmentation to be effective?

a.Measurable: The attributes or characteristics of segmentation should be measurable.

b.Accesible: The segment should be within reach of the target consumers. For eg. a Montessori school in my locality has students attending the school from the nearby areas itself.

c.Differentiable: The segments should be separable from each other. For eg. if it is on basis of area then market maybe segmented on basis of north zone,south zone, east or west zone.

d.Feasible: The segment should be backed by sufficient finance as well as the human resources .