# How to go about creating an "inaccurate" map?

We have a professional cartographer, who travels, creates maps, duplicates them, and sells them to people as he travels. Unfortunately, he is not the best at his job - and he has nothing other than a compass, paper, and quill (and ink).

I would like his mistakes to be somewhat meaningful -

"meaningful" defined as: mistakes which would cost a traveler time in figuring out there was a mistake and in having to figure out the correct action in order to get to where they were intending to go

What accidental (or on-purpose, but he still intends the map to be useful to anyone who may use it) mistakes would most affect a traveler who is trying to use the map, yet still seem correct to people who are vaguely familiar with the area?

As suggested in the meta question, the best answer will be the method that is most wrong and least obvious to inhabitants.

• But if travel is overland and mostly by roads, rivers, ridgelines, cartpaths, game trails, or other visible landmarks, then scale inconsistency doesn't affect the ability to get from one place to another very much. What it does affect is the discovery that two places visited on different trips are near each other. Imagine piecing together a map of the US from AAA's old trip-tick style maps which were narrow strips that followed a highway (drawn along the center line) showing whatever happened to be a mile or so to either side, but where each strip got the scale wrong. Commented Jun 8, 2015 at 20:59
• @RBerteig Another example is public transport maps such as the famous London Underground map, where the map conveys which lines go through which station but do not accurately conveys how far apart stations are. Commented Jun 8, 2015 at 22:08
• just be inaccurate. Take a real map, consider the journey between two locations. Now make every measurement randomly wrong by a couple of %. So the distance won't be exactly 10 miles, it'll be 10.2 miles, do the same for angles. Soon, your map will be authentically 'wonky' as desired without being completely artificial. Commented Jun 9, 2015 at 8:38
• I read "meaningful mistake" in this context as "significant mistake" - a mistake which actually matters. If that is the intended meaning it may reduce confusion to edit the question to reflect that. Commented Jun 10, 2015 at 2:00
• The recent edit makes this a valid question now since answers can be objectively judged. I've voted to reopen. Commented Jun 11, 2015 at 18:58

If you look at historic maps (eg. this map of Europe from 1572), shapes are locally accurate and shorter distances are generally correct. However, if you try to combine this local information into a large-area map, small errors in distance and direction add up, giving a distorted overall picture.

One way to get this effect is to mix up map projections. For example, you could draw the map using a distance-preserving projection such as equirectangular, then treat it as if it were a conformal (angle-preserving) projection such as Mercator or an area-preserving projection such as Gall-Peters.

• In the same vein, there's a quote somewhere from Louis XIV about how, because of the discovery of an accurate way to measure longitude using the moons of Jupiter, he was "losing more territory to his astronomers than to his enemies." Commented Jun 10, 2015 at 2:07

Perhaps his trap streets have gotten away from him.

These are intentional errors added by cartographers to prevent someone from copying their work and getting away with it. After all, if everyone described an area perfectly, how could you tell the work apart? If your cartographer is particularly worried about theft he might be letting too many of these intentional fake streets, lakes, or whatever into his maps.

Not that accidental mistakes wouldn't exist already with such simple tools. Several mistakes are easy to make:

• [Directions] The particular cardinal direction a road heads off in (if it gently curves over two miles, that's hard to accurately map without taking a lot of data points).
• [Distance] How far from the river the fork in the road actually is (without a measuring wheel, all he has is the counting of steps, hard to do in mud or hills)
• [Names] The name of that small farm he didn't bother to check with the farmer (Old Flabby's Farm might only be what his ex-wife calls the place). Or the river one local has named after himself (Who else can he check with about Bob's River?).
• [Elevation] Without a reference point or some fairly good measuring equipment he can only estimate elevation by grade/distance measurements or educated guesses (Is that a mountain or a hill?).
• [Math] Compass measurements and distance alone won't make an accurate map, in order to combine map parts mapped at different times or to accurately judge the length of a curving road, he'll need to do some tricky math without a calculator (Hopefully he's good at trigonometry in his head).
• The trap street idea is really cool. This could be used for some pretty interesting plot devices too. Commented Jun 8, 2015 at 21:38
• @Martin_xs6 Or it could be that he copies other maps, but is completely oblivious to all the trap streets he copies. Commented Jun 8, 2015 at 22:49
• @DavidMulder They, and other such copyright traps, have been in use for a long time, a cursory investigation shows at least one example as far back as the 1930's. Not sure where you pulled that comment out from, but it doesn't appear to be a well reasoned claim. Commented Jun 9, 2015 at 19:15
• @DavidMulder I could see trap streets making sense in a medieval/fantasy setting too, where maps are always drawn entirely by hand -- why would Shady Joe bother mapping out a given region himself if he can just spend a night hand-copying Goofy Gary's map line-for-line and sell it for only a slightly cheaper price despite the fact that he did much less work? Goofy Gary may not be accurate, but he still takes pride in his work and wants to protect it, so he starts adding trap streets (or the regionally-sensible equivalent; perhaps a fork of a river that doesn't exist). Commented Jun 9, 2015 at 19:15
• @DavidMulder None of that makes any sense. A map maker can check a competitor's maps by walking down a ways in the market to their shop and looking at their maps for sale. A map maker can register their maps with the local authorities who are there to protect merchants. Sure, you can make up a situation where it doesn't work, but if the map maker removes the trap they have zero options for even attempting to prove someone copied their maps. Commented Jun 9, 2015 at 19:30

He omits details he doesn't think are important.
He's traveled so much that small landmarks no longer impress him.
Surely that pond isn't important. This road might as well not have had a bend there, it gets to the same place. That hill isn't big enough to be worth noting.

• ...wow, that's a terrible cartographer. Commented Jun 8, 2015 at 23:37
• @Leushenko, not really; ancient maps were more about landmarks and schematics ("How long does it take to get to Rome, and which turnings do I take?") rather than precise detail. Leaving out various bits and bobs would be typical. sitemaker.umich.edu/mladjov/maps& Commented Jun 8, 2015 at 23:46
• Not to mention, cartographers do this nowadays. They have to, or no maps would exist. Thanks, Mandelbrot! Commented Jun 9, 2015 at 19:33
• @PaulMarshall Ah, I wanted to see that link again and it's broken :( Commented Oct 31, 2016 at 22:23
• @DoubleDouble That map project is gone, but here's the map that was at the top of the page: crystalinks.com/RomeRoadsItinerarium.jpg Commented Oct 31, 2016 at 23:40

He could have an iron ring on one hand. Then, as he travels and checks his compass, he could sometimes use that hand to hold his compass. The ring, being magnetic, would make the compass point a different direction, sometimes significantly messing up his map. (This would also happen if there was enough iron (or a magnet) close to him. He could have an iron or magnetic pendant that could also do it.)

He could also be making maps in a region with magnetic field perturbations. This would also cause his compass to point in the wrong direction, and would be pretty hard to detect without more advance equipment.

(More on magnetic deviation here: Magnetic deviation )

Lastly, perhaps the area he traveled in could have multiple different measurement standards. Depending on who he talked to, a 'meter' or 'mile' or whatever, could have a few different meanings. If he was a bad cartographer and didn't know this, he could copy maps with differing 'mile' measurements, causing his master map (and any maps copied from it) to be of an inconsistent scale.

Depending on the era of your setting, over larger distances he might have very great difficulty getting an accurate fix on his longitude. While latitude is easy to measure for anyone who knows how (you need a sextant or astrolabe; no problem for ancient technology), and would allow his maps to be accurate in the north-south axis, longitude requires you to accurately calculate the time in some fashion, which is more difficult for a lone traveller with limited funds if he lives before the era of precision watchmaking.

He would need to carry an almanac and measure his position astronomically, which would be potentially expensive and time-consuming, so he can't check it very often. If he loses the almanac to bandits or poor weather or something, his map will suffer a discontinuity until the next town large enough to buy another one, because he won't be able to whip up his own (his observation tools could be replaced by a smith if he has the money, but the tables require advanced astronomy, and that means a city or port).

As a result, the maps will potentially be all over the place in the east-west axis, zeroing in on major towns and cities when he gets to them, and distorting by bigger and bigger degrees along the more dangerous or difficult roads.

Perhaps he never remembers to write down the scale. This would cause mispositioned buildings, longer streets, possibly even disfigured structures if they're large enough.

Distort the shape of things instead of the scale. This would work best for something other than a road, maybe a river or mountain range. Making them significantly more or less straight can leave out potentially significant amounts of landscape, or create non-existent areas on the map. It's also easy to do when you're not right up on it.

With the tools you give him (compass basically) you can find directions, but have no sure way to measure distances. So he might be very observant, but over time some mistake may be present. Especially if a travel is more difficult (difficult terrain or weather) the distance might be entered as bigger than it is. Also as a traveller you only see the part around you, setting it all together is extremely difficult without aerial observation. Also in the middle ages scenario people might not be aware about the earth being a sphere and therefore landscape doesn't fit on a plain map without a transformation. All these errors can add up. You can look at historical maps to get an impression:

• Distance measurement is especially easy to mess up if there are no fixed measurements (e.g. milestones) and he has to measure by paces. Assume three cities A,B, and C with a straight-ish road that connects A and C, and a more-or-less perpendicular road off it that connects to B. If he maps A->B in good weather and counts 2800 paces to the fork, but it's raining when he maps B->C and he takes smaller steps going through the mud and gets 3200 from the fork to C, he will incorrectly calculate the route from A->C as being 6000 paces... (cont'd) Commented Jun 9, 2015 at 19:22
• ... so rather than plotting the A->C map separately, he just derives it from combining his A->B and B->C map. Perhaps he does calculations based on his stride measuring 2.5 feet, even though he only slogged along at about 1.5 feet per stride in the mud; his A->C map would indicate a distance along the road of about 2.8 miles when it was really only ~2.2 miles! Or perhaps he calculated his stride while on his path from B->C, and used that for building his map for A->C: he's come up with 1.7 miles -- imagine a buyer's frustration when they find out the city is half a mile further away! Commented Jun 9, 2015 at 19:38

While it doesn't precisely depend on the cartographer's mistakes, environmental changes could lead to his maps becoming outdated/inaccurate. Fires and floods could easily alter, relocate, or entirely destroy things he may have identified as vital landmarks.

If the cartographer then returns to such an area (especially if he approaches it from a new direction) he may not even recognize it as the place he mapped and would thus re-map it, assuming it to be a new location near the original one. Combined with some scaling issues, this could lead to the same locale being represented in two wildly different locations on the large map (this also makes the issue his own mistakes rather than uncontrollable, unforeseeable events).

People tend to make things bigger, more detailed, more prominent, etc. if they are important to them. That's why most maps made in Europe or North America put the Atlantic Ocean at the center, whereas Japan puts the Pacific in center place. Australians put their maps "Upside Down" relative to people in, say, England, where North is up. On older maps, the country of origin of the map maker is usually inflated. Old maps of Europe are notorious for this. Many people make maps to be symbolic rather than functional, which is why older maps sometimes use the "T and O style, where the oceans are a ring, with Europe, Africa, and Asia being separated by a watery "T" representing either different seas or sometimes rivers. Jerusalem is usually centered on these maps, with East on top and Gibraltar (the "Pillars of Heracles") at the bottom. Also, unexplored regions are often completely left off maps, with seas and coasts abruptly ending, usually save for a label, like "Parts Unknown," or in one famous example that's made a definite cultural impression, "HIC SUNT DRACONES."

Hope this helps!

EDIT: I have been informed that the South-up map orientation isn't as common as I thought! Turns out that's a newer thing. Also, here are some sources for visuals:

Inflated Europe: https://commons.wikimedia.org/wiki/File:Oceanus-hyperboreus.jpg

Parts Unknown and "HIC SUNT DRACONES" (Note: There is only one known map to have unironically used this phrase): https://twitter.com/mmoinks/status/990397919915323393 https://en.wikipedia.org/wiki/Terra_incognita https://whereisyvette.com/2014/01/31/maps-from-parts-unknown/ https://en.wikipedia.org/wiki/Here_be_dragons

– JBH
Commented Mar 28, 2019 at 23:51
• Welcome to Worldbuilding, Cynthia. Your answer appears to make a lot of assertions with little evidence; I for one have never seen the 'upside-down' maps in Australia you describe, and I have lived in Australia all my life. Could you please provide some references or links to examples for the assertions you make? Commented Mar 28, 2019 at 23:51
• Of course! I'll provide some sources. Commented Mar 29, 2019 at 12:24

The map-maker might live in an age where the written language is not very prescriptive. Words and unfamiliar proper nouns ("McLaughlin's farm" could become "Maclaflin's farm") would be written as best the map-maker could understand them, in a sort of personal pidgin. (Or if the map-maker knew the correct spelling, he might corrupt them and simplify them so his intended customers could read them.)

When making maps or describing routes most things "make sense" if you are familiar with the area or route yourself, but a small discrepancy can mean big differences.

If he is making "maps" of routes he has travelled they are not going to be like the kind of triangulated map that we expect, but more likely a long tape with the way points marked, using the compass he should accurately be able to mark which direction people should take.

The main thing that would cause discrepancies would be anything obvious to a local.

e.g. the map says to follow the road North West from the village past the Millers Family farm and keep going for half a day... etc... At Millers Farm there might be two paths, one that is the correct one and the other that is used by the sheep so seems bigger and better... everyone local knows which one to take and it seemed obvious to your cartographer that the other was to the sheep dip only, so he didn't mark this navigation point. Poor Bill buys the map but he's never been out of the city so doesn't know what a sheep looks like let alone a sheep track... used to travelling on the roads he sees the big track and heads down it... half a day later he's at the sheep dip, not the village; with no idea where he went wrong and no tent...

Also changes in the landscape might invalidate his locations/waypoints... that rotten oak might fall completely, that ford could be washed away, but the locals would still know where they had been so wouldn't spot the error

Also: Distances might not be measured as distances but in times. I took our man half a day to travel it, but was that half a summer day? How fast did he walk? I imagine

Historical map inaccuracies often included guesswork that was not clearly marked as such, leading (for instance) to an implication (or even assertion) that one large island was two small islands, or vice versa. A road branching off of his map of the road from A to B might be labelled as going to C just because he knows C is in that direction, even though the road in fact goes around the nearby mountain and then stops at D, which he's never heard of.

It also depends how careful he's trying to be. Is he drawing the maps as he goes? Or only at night drawing in the map of the day, in which case he's likely to forget details, or put things in the wrong order?

As an exercise, try drawing some maps from memory of trips you take. You'll likely find that you draw roads with fewer bends than they really have, and over-estimate the degree of the bends you do draw. If you draw cross-streets, you'll leave some out or get them in the wrong order; if you try to draw the stoplights and stop signs, you'll probably get some of them wrong. (While he might live in a world without stop signs, he probably lives in a world that care a lot more about the depth and speed of a river or creek that crosses the road.)

What sorts of errors accrue, and how significant they are, depend a lot on his intent in these maps. Simplifying out the bends in a road might be completely legitimate, if the point is just to follow the landmarks and turnoffs to get from one city to another when the road is not direct. But forgetting a crossroad or being off by a few degrees will make a huge difference if his instruction is "turn north at the third crossroad".

Create an accurate, exact map.

Describe that map to someone else using words only. Talk for 10 minutes with them drawing the map during that time.

Give what they create as the inaccurate map.

For less accuracy, take 5 minutes to describe it, and then give them 5 minutes to draw it

It will introduce many inaccuracies. Many of which are similar to what would exist in inaccurate maps: Placenames can be mispelled. Lengths, areas and positions of features will be innaccurate, less important details will be omitted. Hopefully, these omissions will be worse in areas that are of less importance, as most people will start by drawing the broad land shape and major features/cities, filling in minor features if they have time.

Some things will simply be wrong, especially if you use the 2nd suggested method (did he say there was a mountain there, or a volcano??).

The two reasons main maps are inaccurate are if the person never saw the features, but is relying on someone else's description, or if they knew, but forgot some or all of the details before they could draw their map - even a rigorous cartographer is unlikely to draw whilst walking.

Inaccuracies due to people being bad at drawing, and making things up can also be present, but this method should include the first of those.

There's a lot to be said for mixing up scale and distance etc... to confuse things but simple count errors with reference to simple landmarks are easy to do and are likely to cause major hassles. To that end mix-and-match the order in which bridges and forks in the road occur, for instance if in reality you cross a bridge and then take the third right to get to Clarke's Crossing then the map should have one of those forks before the bridge and the third right will be miles further down the road and take you to Valport. If you do this with multiple bridges, or other landmarks, and road forks the whole thing will turn into a complete mess very rapidly and working out where you are based on what you have and haven't passed is almost impossible. It's still a rather subtle mess because it's only really in conjunction with directions that it becomes obvious that there's a problem.