How is Project Scope different in 'Project Charter' different from Project Scope in 'Project Plan' considering they both have to be brief ... isn't it redundant ?
Project charter is part of the initiation phase; project plan is part of project planning. The scope should be substantially the same in both places. The scope is so important to the success of the project that (literally) it bears repeating.
If the project scope is well defined in the project charter, then it is possible to simply copy it into the project plan. In a perfect world, the scope in the project plan could merely be a reference to the scope in the charter; in the real world it is frequently necessary to be more specific or to address the scope in more detail. In the scope section of my project plan I am more likely to explicitly address issues that are out of scope, or to clarify the boundaries of specific activities. There are times when I revise the wording of the scope to facilitate planning.
There are also cases where some other document serves the purpose of the charter (sometimes the Statement of Work serves as a charter; in one of the project management methodologies they use a project initiation document).
In any case the project plan should emerge from and terminate in the scope (the scope, the whole scope and nothing but the scope.
They are redundant if you are authoring both documents at the same time, but the PMBOK process is designed so that the Charter would be done first, reviewed, updated, resubmitted, and approved before the Project Plan would be started. After the Charter is approved, through your activities in finalizing the project plan, you should be able to able to provide more detail to the scope of work over what was included in the Charter.
The way I've done this is to keep the scope in the Charter very high level (E.g. "Renovate reception area") but provide a nother level of detail in the Project Plan (E.g. "Renovate reception area by: 1) painting all walls 2) replacing the carpet 3) installing new signs" ). If you are authoring both documents at the same time, you could document the scope in an external document and refer to it from both the Charter and the Project Plan.
The answer has been really covered in the above posts but I would like to link it to the concept of "progressive-elaboration". The level of detail available (and hence provided) at the time of charter is generally not as in-depth as it would be at the time of planning. Hence, although brief, the level of detail will be more during planning phase.
The charter project scope is general enough for sponsors to agree upon; the the PMP project scope is detailed enough for the PM to meet expectations.
RATIONALE: The charter is a treaty. You get the sponsors to nail down commitment, budget, resources, and target (scope). They decide under what terms they consider project done, what conditions to cancel, and what strategic phase gates to consider. Work out a draft critical path. They sign it. This covers the PM's back.
The PMP is a technical extension of the charter. It ties down all the other pieces such as integrated schedule, RACI, risk/issue tracking approach, etc.
The charter scope gets written first; when sponsors are committed, then start the PMP and progressive elaboration/requirements. You may want to look up the BABOK 2.0 - the PMBOK only goes so far.
SOURCE: Personal experience as project manager/supervisor with government software projects ranging from $2.5m up and the need to protect my PM's from project scope issues.