# Areas and categories > Johnny.Decimal areas and categories, the two digits before the decimal, define a system's structure. ## What is an area? Areas are the filing cabinets we just talked about. Think of them as 'areas of your life' or 'areas of expertise'. That's how broad they should be. If they're too narrow, you'll use them up. Leave room for expansion. ### Areas group categories Area `10-19` groups all of the categories from `10` through `19`.[^zero] Everything also has a title, so this becomes `10-19 Life admin`. [^zero]: Area `00-09` does exist; I'll discuss it later in the advanced topics. Similarly, area `20-29 Home business` groups the categories `20` to `29`. And area `30-39 Tennis club` groups the categories `30` to `39`. ## What is a category? Categories are the drawers we just talked about. They're collections of similar stuff: travel documents; marketing material for your small business; facilities maintenance for the tennis club. And they're the most important Johnny.Decimal concept. ### Categories group IDs A category is as organised as you need to be. When you get there, you see a bunch of ID folders. But they all relate to the same thing. And they're ordered in the sequence that you created them. ### A category is where you work Any type of 'work' you do can become a category. When you sit down at your computer you have a task in mind – researching a holiday, writing a flyer for your business, employing a new groundskeeper. The goal of Johnny.Decimal is to get you to the place where you do this work, quickly, with no stress. ### Prefer fewer, broader categories If you have granular categories called `investments`, `budget`, and `savings`, you've created ambiguity. This slows you down because there's more decisions to make. Compress them in to one – `money` – and the ambiguity disappears. ### Categorising is worth the effort Categorising our stuff requires some effort. But it is necessary because it helps us find things again. And it can feel harder when things could go either way. For example, do I go with `Insurance > Car` and `Insurance > House` or
`Car > Insurance` and `House > Insurance`? In reality, you just decide. It's not like you're ever paralysed with indecision: that's the entire point of the structure of Johnny.Decimal. ## Making areas and categories There's two main approaches to sorting the stuff in your life when designing a Johnny.Decimal system. - Top-down: sort everything into areas first, then divide those into categories. - Bottom-up: sort everything into categories, then group those categories in to areas. I talk more about this in the [Workshop](/jdu/workshop/).