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Sometimes, a person might wish to know the touch scale of a map, whether made by another person or you, in order to better understand the world a story is taking place. How might one go about deducing the size and scale of a map from the map itself and any information provided by the author or source material? To be clear, I'm asking if there is any known set of "rules" or general advice for doing this. Common sense sort of stuff and where I should look.

For example, I am currently taking study of the map of the Southern Kingdoms from the book series Guardians of Ga'Hoole by Kathryn Lasky. The scale seems built-in, but I am unsure of where to begin the figure that at, such as knowing what in the real world it can be compared to. (I'm not trying to make anyone do it for me, just trying to gather information on how I can do it as well as more maps in the future).

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    $\begingroup$ I'm not sure this question is entirely about worldbuilding, so it does risk being closed as offtopic. The map you've attached seems mostly diagrammatic, though, so there's no guarantee that any part of it is to any particular scale. You'd need to read the text and see if it described journey time between landmarks that appear on the map, and try to estimate at least local scale from that. Non-trivial though, and very low accuracy. $\endgroup$
    – Starfish Prime
    May 24 at 9:45
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    $\begingroup$ (I wonder if it might be better received on the scifi&fantasy stack exchange) $\endgroup$
    – Starfish Prime
    May 24 at 9:47
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    $\begingroup$ Generally, you need a reference distance. In this case, you'd need to search through the books, and find a section that discusses how long it will take to cross a certain area/distance and then you can calculate from there. In your example, If you found a line that stated "It takes 10 days of continuous flying to cross the desert of Kuneer" or whatever, you could then use figures of owl flight speed to calculate distances and establish scale. $\endgroup$
    – Dragongeek
    May 24 at 10:25
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    $\begingroup$ @StarfishPrime - The question of how fantasy maps can be scaled in general would be off-topic ("too broad") for SFF:SE. That being said, the question of scale regarding this specific map would be on-topic and very answerable. $\endgroup$
    – Richard
    May 25 at 20:25
  • $\begingroup$ @StarfishPrime - I've not read the books in any detail, but a very quick glance reveals that the measurements used are leagues and feet (which is common for fantasy novels). There are multiple references to things being x days flight. It should be pretty straightforward to find various objects that are x distance being y days flight, giving us a scale to use as a measure, although I highly doubt that the map is in any way consistent with the books $\endgroup$
    – Richard
    May 25 at 20:38

4 Answers 4

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Travel time.

Mostly maps for the books are made because position and size of various regions matters to the story. Let's say a hero travels by foot from town A to town B following specific path on the map. There is a description of the journey, so you may know how fast he traveled and how long it took. Make the estimates, it will give you an upper and lower bound for map scale. If here are multiple travels, you can adjust the scale accordingly.

Sometimes the book just says something like "town X is 3 days from the capital by coach" or "troops from Y will arrive to Z in a week".

Guardians of Ga'Hoole is about owls. They fly. Same logic applies, except you don't have to worry about the roads. Read about owls, find out their speed range, multiply it by travel time - you have an approximate map distance between A and B.

It is rough, but it's not like precision matters much. Consistency is not the main priority in world building for fantasy books, it's more about story and characters.

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    $\begingroup$ Owls might not have to worry about roads, but if (as a previous comment suggested) if took 10 days to fly across a desert, this might be prohibitive because an owl isn't going to be able to fly 10 days without rest and food, and those might be difficult to find in a desert. Not all terrain is equal in terms of speed of traversal, even to flying creatures without obstacles. $\endgroup$
    – Darrel Hoffman
    May 25 at 18:09
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Look for the market towns in populated agricultural areas. Since everyone needs to be within a day’s travel of market, those towns should be around 15 to 20 miles apart, as they are in Europe. This method will show that many fantasy maps, e.g. Westeros, are far smaller than measurements derived from other methods, but that’s because the author has created an inconsistent world.

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    $\begingroup$ Or that not all market towns are shown. $\endgroup$
    – elemtilas
    May 24 at 18:36
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    $\begingroup$ @elemtilas Definitely an important point. If I open google maps and look at, say, France, at the largest 50km scale, I see at most 1 town every ~50km - for example I see just an empty road between Le Mans and Orléans. But if I zoom in I can see there's actually a small villages every ~5km along that route, and slightly larger towns every ~10km that would probably equate to market towns. When I'm drawing maps, unless it's a small-scale regional map, I'm not going to include places like that unless they're specifically relevant to the story. $\endgroup$
    – Kayndarr
    May 24 at 23:58
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Without an explicit scale length or descriptions from the text, you're limited to comparison with real-world topography and extremely rough estimates. These will vary substantially dependent on:

  • The details of the world being described, including technological level and climate.
  • How familiar the author / mapmaker is with real-world geography and whether they felt the need to make their world consistent. It's entirely possible, even likely that the "hard-science" tag you've placed implies more research & consistency than was intended when the map was made.
  • Whether the map is intended to be an accurate 2D projection of the world, or whether it's more intended to be a notional / somewhat abstract guide like many real-world pre-15th-century maps.

For instance, in this map:

  • you have an inland sea / lake in the north with rivers at both the inflow- and outflow-. There are also several lakes / inland seas with outflowing rivers. Look up the dimensions and total surface area of the Great Lakes in North America. Those have rivers at both inflow and outflow, rather than having extended bays or gulfs, so might be good analogs for what's depicted. Larger bodies of water will presumably be connected by channels or will be entirely separate (like the Dead Sea). Smaller bodies of water would presumably not be drawn at all, or be subsumed into the single-pixel-width rivers.
  • This map has no obvious polar regions or distortions due to a curved spherical surface, so either the world is very different from ours, or you're looking at a region with dimensions much less than that of the Earth. Comparison with real-world continents should set some upper limits on the scale. (Well, the "Ice Narrows" sounds like it might be at a similar latitude to Scandinavia, and the "Desert of Kuneer" sounds like a notional reference to Arabia, so the north-south distance on this map might be comparable to Europe.)
  • The rivers are as narrow as the map-maker could make them, but have definite lengths. Compare the length and width of the Mississippi or other major continent-scale rivers (the Nile, the Rhine, the Ganges, the Amazon, etc.) and measure the distribution of lengths as best you can in the map. At some point, depending on rainfall and drainage area, rivers would turn into finite-width bays / sounds. Getting an idea of how large rivers tend to be before it's necessary to worry about their width on maps will set a minimum resolution. One pixel on that map is likely a mile or two across, possibly more. If it was significantly less, I'd expect the rivers to have finite width.
  • Assuming medieval-ish technology, most countries are probably only a few days' or weeks' travel across by horse. Any larger and merchants & soldiers & messengers can't keep the different parts of the kingdom in touch. Loose confederations and empires that take tribute from their subsidiaries but don't directly manage them can be larger. Compare the sizes of your nations with those of real-world countries from a similar technological level.
  • All of the cities marked on the map seem to be points or fairly small dots, and many countries don't appear to have any at all. Compare the scale of the largest cities from the real-world at a similar time period / tech level. If the people living inside cities have to get fresh vegetables from the countryside via a local market, then the city radius is going to be limited to perhaps a day's travel on foot or by horse-drawn wagon... probably half that or less. Larger regions will require gardens / farms in the middle of the city, making them more like clusters of towns than "cities". Analogous constraints will apply for fresh water supply, drainage of rain, removal of sewage & trash, etc. Cities that are more than a few dozen miles across require significant infrastructure not available before about the 20th century.
  • You've got several regions marked as "forest" or "desert" or similar. Compare those regions with similarly-uniform concepts in the real world. "Barrens" and "badlands" tend not to be huge. Mountain ranges tend to be dozens- to hundreds- of miles wide and hundreds- to thousands- of miles long. "Forests" and "Deserts" may range from perhaps 50 miles across to continent-scale affairs, but you don't often see rapid transitions between forest & desert without a natural barrier (e.g. mountain ranges). Look for such transitions in your map. If the "Desert of Kuneer" and "Forest Kingdom of Tyto" don't have obvious regions for the differences in climate, then the distances between their centers might be something on the scale of Texas or larger, with deserts in the west and forests in the east.

All this is going to give you an array of estimates, upper limits, and lower limits on the map scale. They may not be consistent. My guess for the given map is that you're looking at something comparable to Europe, but I haven't run any of the numbers, and the original author might've intended something different.

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Trigonometry

If the map is accurate at al for overland navigation, it needs to be somewhat consistent in two directions, and thus is often some kind of projection that is somewhat good for angles.

Now we need exactly one length, and everything else can be solved using Tigonometry: $$\sin \alpha = \frac a c\ ;\ \cos \alpha = \frac b c\ ;\ \tan \alpha = \frac a b$$ That's easy to solve for b and c, we just need the angle of one tip and everything starts to solve, and you will learn how long the distance between two more points is, and in the end you can map out the distance between any two points by trigonometry. The quality of your calculations is based on three factors though:

  • your initial length measurement
  • your ability to measure angles correctly
  • the quality of the map when it comes to the angles being represented correctly

The initial length

Now, we need to know the initial lenth. How can you estimate that? In general, you can do so from the accompanying text.

For example, the rulebooks for the game Legend of the five Rings describe the distance between Kakita Castle and the capital as "a day's ride". That is not very precise, but can be a good starting point. Assuming that is a distance without a horse swap, we're faced with about 10 hours of riding (including a break in the middle), and a horse travels at roughly 3 miles per hour, so the distance is roughly 30 miles along roads. If the distance however is meant to be rapidly with horse swaps (like how postal service did!) a day worth in post riders is much further and for example the Pony Express traveled at an average of 12.5 miles per hour for 10 hours, so the two places would be about 120 miles apart, if that is a day's ride of the pony express.

Similarly, you might know how long it takes a military unit to march from one town to another. The typical, normal marching distance per day for an army that starts day with breaking camp and ends the day with setting up camp can be estimated quite differently. Estimates for the Roman Army swing widely, but typically are claimed between 30 and 40 kilometers, the typical average being about 35 km a day - or about 21 miles. That measurement can be taken generally as a good estimate to calculate distances between towns for any group that is not making extreme haste and is bound to the speed of a marching human.

If your predominant species is flying, measurements get much better by the way: they don't need to curve around terrain quite as much and thus the quality of the initial length is much better than with any ground based species. You just need to figure out how far they march in an average day. For example, the average Stork migrates in average 300 kilometers (~210 miles) per day during migratory season.

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  • $\begingroup$ @NuclearHoagie trigonometry allows to do it all from one length measurement and then only measuring angles, which are usually better to measure than lengths. $\endgroup$
    – Trish
    May 24 at 19:27

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