[talk-au] Fwd: Classifying settlements (Was Re: Filling in blank space (Was Re: Tagging towns by relative importance, not just population size))

[Andrew Davidson]

On 6/10/23 18:14, Little Maps wrote:
> Thanks Graeme, it’ll be great to hear what others think too. Cheers Ian

The first thing to keep in mind is how concentrated the AU population 
is. Sydney and Melbourne both have 20% of the population living in them. 
If we add on Brisbane we reach the 50% mark, which means the majority of 
people live in one of three cities. As a result there is not much to go 
around for the rest.

If we adopted 50,000 as the cutoff for a city we're going to more than 
halve the number of currently mapped cities. 50,000 might work for the 
US (and is also the value the UN has adopted for global comparisons) but 
it's too big for AU. At the other end 15,000 is too small, we'd end up 
creating an additional 25% of cities.

I would suggest that we adopt the ABS's threshold of 20,000. This is the 
population level at which they consider a settlement starts to have 
"gravity" and pulls in surrounding urban areas. It used to be 30,000 
back in the early days of their methodology but I assume they think 
people are more mobile so the "pull in" starts earlier now. 20,000 also 
has the benefit of not changing the number of cities we have by much. 10 
currently mapped cities would become towns and 13 current towns would 
become cities.

For towns the US threshold of 10,000 is way too crazy high. There are 
1,000+ things currently mapped as towns. If we adopted 10,0000 this 
would drop to 101. Even 5,000 would only get that to 198.

I was thinking that we would just use the ABS's UCL list. This divides 
settlements into urban centres and urban localities. If a settlement is 
on the urban centres list and its population is over 20,000, then that's 
a city, otherwise it would be a town. In effect this is a cutoff of 
1,000, which the ABS has used for more than 50 years suggesting that 
it's getting relatively smaller over time.

The urban localities would be villages (a lower cutoff of ~200) and 
settlements not on the list hamlets.

The bigger shifts are going to be in the towns and villages. The UCL has 
(using the rules above):

72 cities
657 towns
1080 villages

but we currently have 1,000+ towns and 1,800+ villages. It is hard to be 
very precise, as these will include place nodes nested inside other 
urban centres and localities.

I looked at the ratio of CTVs from the US/CA/NZ on the assumption that 
being new world settlements the ratios should be similar. The 9 towns 
for each city in AU is similar to the others 7/9/8. What is different is 
the ratio of villages to towns. AU is 1.6 the others 2.4/4.0/2.3, which 
suggests:

1. There are a lot of villages in CA
2. Settlements in AU are more thinly spread.
3. 200 might be too high. The problem being it is a lot of work to get 
population numbers for places too small to register on the UCL.