Per-system numbering

The standard convention builds each alias on the one before it, so a hole three jumps out reads 213. Some groups would rather keep every name short: each system numbers its own holes 1, 2, 3, and one further out starts at 1 again. A manager can switch the map to this in Map settings → Naming → Strategy → Per system.

Like switching schemes, this only changes what the mapper suggests from then on. Nothing already on the map is renamed.

The convention

Each system numbers its own holes: home's are 1, 2, 3; the holes inside its 1 are 1, 2 again, and so are the ones inside its 2.
The way you came in doesn't count: the hole back toward home is not one of a system's own, so it never takes a number from them.
Freed numbers are reused: with 1 and 3 left after the 2 was rolled, the next hole is 2.
The alphabetical scheme works the same way with letters, A, B, C, and k-space exits take their reserved letter and a number, H1, H2.

Set a home system

A chain alias says which way home is on its own: 21 sits inside 2. A per-system 1 doesn't, so the mapper works the way home out from the map instead, and for that it needs a home system. With one set:

the bookmark back toward home gets the return format (*1 ABC C5 by default), the same as in the standard convention;
a system's parent is never counted among its children.

Without a home system, the mapper can't tell a system's parent from its children, so the parent's number counts as taken and a first hole may be suggested as 2.

Example

Home has two holes, 1 and 2. Inside the 1 there are two more:

Home
├── 1   (C5)
│   ├── 1   (C6)
│   └── 2   (C4)
└── 2   (C5)

Standing in the C6, the bookmark back to its parent reads *1 …: it's a return, so it gets the return format even though both are called 1.

Naming it your own way

Per-system numbering and the standard convention are both strategies, and more can be added. If your group uses a convention neither covers, see "Your own naming convention" under Contributing.