That's an interesting association between population and surveying time that I'd not thought of ... I take it the "population about 15,000 so about 15 hours of surveying" is a rule of thumb for urban areas. Do you have any other similar rules of thumb for other types of areas?

By surveying time -is that driving, cycling, or walking? Is that just the time out on the ground or does it include the time to put the data into OSM, make ways, tag things, etc?

I'm just wondering if there's something here in your experience that I could use to make an estimate of how much effort to map the area I am working in.