Relying on an excellent article at http://www222.pair.com/sjohn/blueroom/demog.htm
I have determined that my working density of 56 people per square mile, overall, is a bit low for the focus of the campaign world. Since, according to the article, Medieval France had 100 pop per square mile, with "Germany" and "Italy" at about 90 pop per square mile and Britain bringing up the bottom at 40 pop per square mile.
Fast forward 2 to 3 centuries and these numbers are going to be higher, with concentrations in certain areas, to be sure, but I am looking for a base to start from.
In the world of Orwell, my campaign world, there are several basic types of terrain depicted on the map, not all are going to be populous, so I will limit myself to the useful ones here.
Clear 60per sq. mile
Hills 30per sq. mile
Forest 20per sq. mile
Heavy Forest 5per sq. mile
Mountains 10per sq. mile
(if a reader has actual numbers based on reality, please let me know, or if you have an RPG sourcebook with this kind of information).
There are forested hills and mountains, but I'll just assume that the addition of trees won't make a huge difference in population density. They might in our world, but I do not have enough data to go on, so for the sake of simplicity, I will assume not.
Of course, there will be locations that will impact population density, namely villages, town, cities. As I am not going to map all of these locations, we'll subsume the presence of villages and smaller towns into Clear, Hills, and Forest areas, and to a lesser degree in Mountains.
Larger towns and cities will be on the world map, so I need to account for those.
Below is a figure for Paris in 1700. It's population was 600k, area was 13.4km, with a density of 44,877 per square km. It's square mile population density was 116,230.
|1700||600,000||13.4||44,877||5.2||116,230||Atlas de Paris|
I'm going to figure that cities will provide a modifier of x1500 down to x200. Since most people tended to congregate near cities, even if they did not live within the city, I am going to apply an area of effect in the hexes around the cities of 4 hexes.
The way this will work is that I will take the base terrain type and then apply a decreasing modifier the further away a hex is from the city, up to four hexes away. This decreasing modifier starts with the hex containing the city itself.
Hexes distant modifier
In the course of looking for date for this post, I came across an article here: http://assets.cambridge.org/97805216/61416/sample/9780521661416ws.pdf that I have yet to fully read and analyze, but it looks as though it will prove useful to me.
Further modifiers should be applied based on proximity to the ocean, a major river, or traffic hub.
Major River x1.5
Traffic hub x1.7
These will be applied to the city modifier if the city is in a hex containing the feature or is adjacent to it.
Thus a city in a clear hex on a coastline is modified determined as 60 (base) x (1500x1.25). Of course, if more than one such feature is present, those will also be included in the calculation. This means that a city in a clear hex containing a major river and is also a traffic hub, it's population is 229,500.
I need to define what a traffic hub is. I think the easiest method is to see if another city or town is on the same road within 10 hexes. This allows the modified area around a city to also have an affect on a city further down the road.
However, not every population center is going to be a city. So the question is, how do I determine the number of cities vs the number of large towns.
Since a tool already exists for RPGs at https://www.rpglibrary.org/utils/meddemog/ I am going take the base land area of 115km per hex (as the tool does not use miles), and multiply that by the number of hexes of the nation on my map. I will then plug in x10 the total land area and set the size of the hexes to 115km. Looking at the lower left, I will see that I have 7 towns and 2 cities (I am ignoring the number of villages), giving me what I need. I will use a base population density of 10, on the tool.
So, now I need a population modifier for towns. Okay, here goes.
0 hexes away x400
1 hexes away x100
2 hexes away x50
3 hexes away x20
5 hexes away x5
I will keep the same modifiers as for ocean, major river, and traffic hub proximity.
Of course, I am open to further suggestions or adjustments based on new data, but least I have a place to start from.