Defining scope of ISO certification

Defining the scope is a management decision, not a technical decision. Look into your organization as a whole. If you can find different groups of customers with very different requirements and expectations, or if you can find different sets of jobs almost independent of the rest of the organization, perhaps your organization can take advantage of certifying just part of it. To certify early, to avoid problems with unorganized customers, to implement ISO 9001 step by step in a complex organization.

For example:

A hospital can decide to certify just the X ray service, and then the blood service, and then …
A manufacturing shoe company can decide to certify just the part of the business that works for uniform shoes and leave out the part that works for fashion

The following material will provide you information about the scope of a quality management system: 

How to define the scope of the QMS according to ISO 9001:2015 - https://advisera.com/9001academy/knowledgebase/how-to-define-the-scope-of-the-qms-according-to-iso-90012015/
- Free webinar on demand - ISO 9001:2015 clause 4 - Context of the organization, interested parties, and scope -
- Free online training ISO 9001:2015 Foundations Course - https://advisera.com/training/iso-9001-foundations-course/
- Book – (where I use the process approach this way) - Discover ISO 9001:2015 Through Practical Examples - https://advisera.com/books/discover-iso-9001-2015-through-practical-examples/