ZIP codes are an emergent property of the mail delivery system. While the author might consider this a bad thing, this makes them "good enough" on multiple axes in practice. They tend to be:
- Well-known (everybody knows their zip code)
- Easily extracted (they're part of every address, no geocoding required)
- Uniform-enough (not perfect, but in most cases close)
- Granular-enough
- Contiguous-enough by travel time
Notably, the alternatives the author proposes all fail on one or more of these:
- Census units: almost nobody knows what census tract they live in, and it can be non-trivial to map from address to tract
- Spatial cells: uneven distribution of population, and arbitrary division of space (boundaries pass right through buildings), and definitely nobody knows what S2 or H3 cell they live in.
- Address: this option doesn't even make sense. Yes, you can geocode addresses, but you still need to aggregate by something.
- Well-known (everybody knows their zip code)
- Easily extracted (they're part of every address, no geocoding required)
- Uniform-enough (not perfect, but in most cases close)
- Granular-enough
- Contiguous-enough by travel time
Notably, the alternatives the author proposes all fail on one or more of these:
- Census units: almost nobody knows what census tract they live in, and it can be non-trivial to map from address to tract
- Spatial cells: uneven distribution of population, and arbitrary division of space (boundaries pass right through buildings), and definitely nobody knows what S2 or H3 cell they live in.
- Address: this option doesn't even make sense. Yes, you can geocode addresses, but you still need to aggregate by something.