Johnny•Decimal

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10-19 Concepts
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11 Core concepts
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11.02
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Areas and categories

Let’s look again at the format of our numbers. It’s crucial that you understand why they look like they do.

The complete Johnny.Decimal number

Just as a reminder, every Johnny.Decimal number looks like this.

23.24    31.70
22.39    13.04
31.71    21.02
22.38    13.03
23.21    23.22
32.56    12.34
12.35    21.01
32.55    23.23

Here are a bunch of random
numbers from a theoretical system.

In words, we have any two digits, followed by a decimal point, followed by two more digits.

Group things together (categories)

Johnny.Decimal is all about grouping similar things together, so let’s start to do that.

The 12 numbers    The 13 numbers
    12.34  12.35      13.03  13.04
 
The 21 numbers    The 22 numbers
    21.01  21.02      22.38  22.39
 
The 23 numbers    The 31 numbers
    23.21  23.22      31.70  31.71
    23.23  23.24
 
The 32 numbers
    32.55  32.56

Do it again (areas)

That’s starting to look more like something organised and a bit less like a bunch of random numbers. Let’s take it one step further.

The 10-19 numbers
   The 12 numbers
       12.34  12.35
   The 13 numbers
       13.03  13.04
 
The 20-29 numbers
   The 21 numbers
       21.01  21.02
   The 22 numbers
       22.38  22.39
   The 23 numbers
       23.21  23.22
       23.23  23.24
 
The 30-39 numbers
   The 31 numbers
       31.70  31.71
   The 32 numbers
       32.55  32.56

Interesting…

You can almost imagine this looking like a set of folders. If you didn’t care about anything except the 22 numbers, you could just collapse the others like this.

Screenshot of macOS Finder showing the numbers from the example above as a nested folder structure.

Of course, we’ve done this backwards

When we decide to organise something with Johnny.Decimal, we don’t start with a bunch of numbers.

We start like this:

  • First, we divide everything in our system in to (at most) ten large buckets of stuff. We call those our areas, and we assign each area a range like 10-19, 20-29 … 90-99.
  • Then, within each area, we break things up again in to (at most) ten more buckets. We call them categories and we assign them numbers like 11, 12 … 19.
  • Finally, we assign each individual thing in our system to a category, and give it a unique number. We start at .01 within each category, and work our way up through the numbers.

Let’s use a small company as an example, and write it out without the numbers.

Folder
This is a...
Finance
AREA
  Tax returns
CATEGORY
  Payroll
CATEGORY
    Jan '23 payroll
UNIQUE THING
    Feb '23 payroll
UNIQUE THING
  Bookkeeping
CATEGORY
 
 
Administration
AREA
  Company registration 
CATEGORY
  Contracts
CATEGORY
    Cleaning contract
UNIQUE THING
    Office lease
UNIQUE THING
  Staffing
CATEGORY
 
 
Marketing
AREA
  ...and so on

All we really do with Johnny.Decimal — and if at this point you’ve realised this and are thinking, “hang on, all he’s done is put numbers in front of things,” well then you’re not far wrong — is put numbers in front of things.1

But this transforms the way you think about and use everything. Trust me.

Let’s put numbers in front of the system we just built above.

Folder
This is a...
10-19 Finance
AREA
   11 Tax returns
CATEGORY
   12 Payroll
CATEGORY
      12.01 Jan '23 payroll
UNIQUE THING
      12.02 Feb '23 payroll
UNIQUE THING
   13 Bookkeeping
CATEGORY
 
 
20-29 Administration
AREA
   21 Company registration
CATEGORY
   22 Contracts
CATEGORY
      22.01 Cleaning contract 
UNIQUE THING
      22.02 Office lease
UNIQUE THING
   23 Staffing
CATEGORY
 
 
30-39 Marketing
AREA
   ...and so on

So long, cursed alphabet

What does this achieve? For one, it’s removed our dependence on the alphabet. The alphabet is a fine thing but it’s a terrible way to sort your files because things move around.2

Today we have:

Administration
Finance
Marketing

and tomorrow the exports department come along and do this:

Administration
Exports         ◀─ new folder
Finance
Marketing

…and Finance isn’t the second thing in the list any more. This sounds like a small thing, but it makes it impossible for your brain to learn where something will be.

The Johnny.Decimal version

This is better:

10-19 Administration
20-29 Finance
30-39 Marketing
40-49 Exports         ◀─ new folder

Because our folders all start with a number, they’ll sort in a very predictable way. This concept applies throughout the system.

20, 60, 30, 90?

At this point you might be wondering, well, why is Finance all of the numbers from 20-29 and why is Exports 40-49? What do those numbers mean?

And the answer is that they mean nothing. They’re just numbers. 40 isn’t better or worse than 20.

In summary

On this page I’ve talked mostly about the way that we structure our areas and categories. By now you should have a good high-level understanding. You have categories of things and each category belongs to one area only. Areas group categories together.

All of this happens before the decimal. Those two digits of the number are the category, and the first digit of the number tells you which area it’s in.

What we’ve done here is organise a bunch of ‘stuff’ in to something with structure; we’ve created, essentially, a very simple database.

Footnotes

  1. I’ve seen countless file systems with numbers in front of folder names, but if they’re not structured it doesn’t work. ↩

  2. This is why people at work naturally put numbers like 01, 02 in front of folders. ↩

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