When creating personas, "why" is the crucial question. Rather than slicing the whole Users population, you should therefore find those who represent a prominent set of strategically important characteristics.
Here is how. The whole population of Users consists of people representing various characteristics. Each of the characteristics can be strong or weak, common or uncommon.
In general, a characteristic becomes important when it is quite common in the whole population, not when it is very strong. For example, in some cases your persona may be a regular, everyday normal guy, for whom most of the characteristics are not at all extreme (average income, average age and so on), but still, this set of characteristics is popular. Or, if you are creating an app for e.g. extreme introverts, between your Users this extreme characteristic would become common.
However, the common nature of some characteristic is not the only one that makes it important. Some Users may be more valuable from the strategic standpoint, which usually means that they are important for Business.
This strategic importance can be defined in various ways: they can be elderly people, people living in Minnesota, administrators of the system you create. In other words, if Business speaks "administrators should be able to..." very often, this means that you probably should create a persona or two within this group, depending on what characteristics groups you find within this kind of group. You may decide to further divide them by gender, age, place they live, whichever has a strategic importance.
At the same time, you may have another persona, who is defined by another characteristic, but not related to their role, e.g. women at their 30s.
To give you an example, if you create a holiday service, allowing people to go to various places around the world, some personas to consider might be:
- Joe, a system administrator because there are a lot of them performing some actions in the system,
- Jane, a part time community administrator because there is another form of cooperation between them and the company,
- Josephine, a 46 y.o. woman with medium to high monthly income, because she is the person who will build up the word of mouth, being an ambassador of your services,
- Marco, a 26 y.o. guy, because he will represent the group making the most of the traffic,
- Lena, a 42 y.o. home owner in Hawaii, because this destination brings the highest income for the company.
And so on.
As you can see, some of them relate to specific roles in the system – something that is quite obvious for administrators, where age, gender etc. may be just additional features to make the persona feel a real person.
In other cases, they may represent only a part of the population within a role, but a part that is important for Business. For example some home owners, living in a specific region and building up the most interest in your services may have some preferences that would not be the same for those in other parts of the world. At the same time the addressees of their home rental services may be a subject of interest of the group that Marco comes from, the one who makes the most of the site traffic.
So, as a wrap up I would say that deciding which personas to create should depend on what is important from the Business (strategy) point of view rather than splitting Users population in some parts.