Crafting Plausible Maps

Building a map for a fantasy setting involves a lot of details – most of them fun! Art styles, fonts, and icons need to be chosen. But some mapping concerns go beyond mere aesthetics. If you’re building a sizable chunk of continent on an Earth-like world,* you’re going to need to keep geology in mind.

Mountains

Mountains are the skeletal system of your world. Unless you already know the exact shape of your continent or island, sketch your mountains before your coastlines.* Mountains back each other up and form chains, ranges, and ridges. They take their shape from their creation:

• Most mountains are the children of lusty continental plates, birthed from scandalous collisions between landmasses too attracted to each other for their own good. The surface crumples upward where the plates collide. Even when one plate slides beneath the other, the friction and pressure send mountains shooting upward.
• Volcanic mountains can form near the edge of the top plate during this long, slow collision. Volcanoes are formed from the recycled remnants of the bottom plate.*
• Plates burning themselves as they migrate over mantle plumes* deep in the planet can also give rise to volcano-blisters. These eventually form chains of mountains as the plate slowly moves over the hotspot.
• Impacts between planets and asteroids form circular rings of mountains. Sometimes an impact crater boasts a second ring or lone peak at the center of the crater. If the crater is big enough and the world is Earth-like, it will likely be a lake or sea.

All four of these methods form chains, ridges, long plateaus, or rings. Lone mountains are rare and almost always volcanic in origin.* Hill country, worn plateaus, badlands, and other rugged-but-not-mountainous terrain is typically the eroded remains of ancient, “dead” mountains.

On Your Map:

Place mountains in rows or long blobs. If you’ve already drawn your coastlines, extend the mountain chains past them, forming peninsulas and island chains. On land, their foothills should be visible: scatter a few hills here and there at the margins of the mountains. A few ranges of lone hills (old, worn out mountain ranges) are a good idea. The occasional lone mountain is okay; it’s probably a volcano or the central peak inside a mountain-ringed impact crater.

If your goal is realistic topography, remember that mountain chains look like long fused ridges at continental scales. Most individual mountains are only discernible when the map is zoomed in to the scale of a small European country or U.S. state.*

Coastlines

Coastlines appear to be the singular, end-all defining feature of any landmass – and to human experience, they are. But a planet’s rock is stalwart and little concerned with its surroundings, whether gaseous atmosphere or liquid ocean. On human timescales (thousands of years or less) water is largely irrelevant to solid land. An island is just a mountain surrounded by ocean, and a mountain is just an island with the water drained down. Any contour line on a topographic map or any depth line on a nautical chart could theoretically be a coastline. So outline your mountains first. Then for your coastlines, just add water.

When water is poured over a landscape formed of continents and mountains, what does it do? Land isn’t arbitrarily arranged on a planet. Plate tectonics sort rock into lighter and heavier, and clumps the lighter rock together as continents. And at any level of magnification closer than a full global picture, coastlines will have a similar, fractal look.

This fractal nature means you can focus on the coast of a small territory or examine the margins of a continent, and the contours* should be about the same. In fact, if you aren’t feeling very inspired, you can take a zoomed-in island from Earth* and make it your fantasy continent, or vice versa.*

But there are some quirky exceptions to the fractal behavior of coastlines, and some places where the shore may look distinctly different:

• Land sorts into large continents from a distant enough perspective, and tidal flats and beaches complicate matters when zoomed far in.
• Mountains, glaciers, and (most importantly) a combination of the two affect coastlines. The glacier-carved fjords, inlets, and island ranges of Chile, British Columbia, and Norway are complex, convoluted affairs. And these regions don’t look the same at all levels of magnification.
• Coastlines also get a bit weird around river deltas. The land bulges outward, but this bulge is carved up by multiple river channels.
• Certain flat regions, like North America’s eastern seaboard, can have complex chains of ever-shifting barrier islands.
• Continents that haven’t had sea-level ice for hundreds of millions of years might have smooth-looking coastlines without a lot of inlets or islands; Africa and Australia are perfect examples.

On Your Map:

• Respect the fact that land likes to clump together into continents; don’t arbitrarily blend land and sea at large scales.*
• Make mountainous coastlines in cold areas – or areas that were once glaciated – especially “fiddly.” Add fjords, inlets, outlying islands, that sort of thing.
• Some occasional long, skinny barrier islands running parallel to the coast but smoother than it, can add a realistic feel.

Otherwise just make sure that most of your coastlines are rough or jagged.

Rivers

Mountains and coastlines follow general patterns but few hard-and-fast rules. Not so with rivers; the courses of rivers are dictated by simple logic and never deviate without a lot of magic. Even the most vigorous hand-waving won’t save you from ridicule if one of your rivers flows uphill or follows a circular loop.

Rivers are like coastlines in that their shape is (arguably) fractal, and their placement is a matter of contour lines. Except that rivers are perpendicular to the contours rather than parallel. Rivers always move along the easiest available path from high elevation to low. And the fractal pattern of rivers is directional: rivers will always merge as they flow toward the coast, never split.*

Rivers often find themselves trapped at the bottoms of massive canyons eroded over millions of years, prisons of their own making. However, rivers are not permanently fixed in place like mountains; they can migrate. Over flat country, meandering rivers shift their course by growing continually wider loops.* Eventually these loops come full circle and “pinch off,” straightening the river once more. But in these scenarios the river stays within its basin. In a mountainous region, a river may change course if rockslides or glaciers block it, forcing the waters to find an entirely new route to the sea. And rivers can be tamed by humans. Even ancient humans frequently diverted rivers along different courses, typically for purposes of irrigation or flood regulation.

Many rivers will be fed by regions with seasonally variant rainfall* or spring melts, and have periods of very low or high (flood-level) flow. As an example, the Fraser is a fairly short river in Western Canada, but during the wet spring, snowmelt combined with massive rainfall gives this river higher flow volumes than the Mississippi, North America’s longest river. Some rivers – especially those winding through hot deserts – may be completely dry and “dead” for part of the year. Or, alternatively, completely frozen.

On Your Map:

Here are some river placement rules, in order of importance from “avoid deviation at all costs” to “explain yourself if you get creative”:

• Rivers never completely cross a continent or other landmass; they never start in the same body of water they empty into!*
• Rivers never form loops. If they appear to, these are actually ring-shaped lakes.
• Major rivers will always end at an ocean or, occasionally, a lake.* Smaller rivers are like people: they can die long, slow, painful deaths in attempted crossings of a vast desert.
• Rivers always join together as they flow toward the sea; they never branch out. Exceptions are made in flat deltas, where the river deposits islands of silt as it empties into an ocean or lake. These are typically small (no bigger than a large city) but can fan out over large distances if the terrain is flat enough. For example, Bangladesh, the world’s eighth-most populous country, consists almost entirely of a single conjoined delta of three large rivers.
• Rivers tend to start at mountains – or occasionally lakes, wetlands, or hills. Mountains catch more water, and they hold significant water as ice that can melt and feed rivers during the spring. If there aren’t any mountains handy, use a forest; these imply sufficient water to found a river.

Lakes

Lakes are generally just a consequence of rivers getting delayed in depressed portions of a continent on their way to the sea. Any time a bowl-shaped, walled-off region exists inside a landmass, its fate depends on how much rain it gets and whether it has a river pouring into it.

If the depressed region is a desert, it will be a dry endorheic basin.* It may have a small salt lake in its bottom, because salts will accumulate over millions of years with no way to escape to an ocean. Or it could have a more recently-filled fresh or brackish lake. If it is rainy or fed by a river, it will fill up until the water can spill out at its lowest point, making a freshwater lake that is part of a larger drainage area.

There’s no real limit on lake size, though continents don’t usually have giant holes in them by default. Earth’s largest lakes have one of two backstories: they were carved recently by glaciers,* or they were formed when pieces of continents began to rift apart.* Rarely, they are water-filled impact craters.

Cold temperate and subarctic regions tend to be peppered with little lakes, connected by a tangle of streams and rivers. This is especially true for cold regions that are rocky over short scales but flat over larger scales. Rockiness means the rivers can’t just carve a straight line through soft ground to their goal. They’re stuck filtering through a series of pools on their way to the ocean. The Canadian Shield* is so dense with lakes and connecting rivers that its “land” is nearly half water.

Like rivers, lakes can shift their boundaries. But when lakes drain or fill, they tend to impact a much larger area. These regional apocalypses can be caused by earthquakes, ice dams, or human intervention.* Consider these as great sources of historical trauma for your world. Any fertile river valley that becomes a lakebed has a good chance of drowning an entire civilization. And any inland sea of freshwater that dries up is also going to bring down a civilization or two, if for different reasons. Both of these things have happened throughout humanity’s early history – if not always on fantastically grand scales.

Less apocalyptic but still interesting are gradual or seasonal changes to a lake’s shoreline. Many lakes, especially in Africa and Australia, fill during monsoons but shrink or empty out during the dry season. This is common in flat regions with shallow, gradual coastlines. Lakes in the mountains might gain or lose similar amounts of water, but their shores are typically so steep they wouldn’t look any different on a map.

On Your Map:

• Treat the coasts of large lakes like a continent’s outer coastline. Any mountain range that ends at a large lake should poke into it a bit, perhaps ending in a few islands. Small lakes are more like little inlets or channels, filling the spaces between mountains and often mimicking rivers in their long, narrow shape.*
• Consider dotted or blurred lines for some lakes, since the shores are not always stable. In regions with glacial ice dams or seasonal monsoon rains, lakes could empty and fill over the course of a year.
• You can pepper cold, wet regions with lakes, especially if the land is flat enough.* But don’t put as many lakes in hot, dry regions unless they’re fed by large rivers. Consider placing salt flats here instead.
• In flat country, consider decorating meandering rivers with elbow lakes. These are remnants of the river’s previous courses; they look like curved pieces of pinched-off river.
• Feel free to string multiple lakes along the course of a river, like beads on a string. This is especially common in cold regions or on rivers held back by dams (natural or human-made).

Vegetation

Not all maps bother to show vegetation cover, but very large plants warrant enough importance to human travel and habitation that fantasy maps will almost always mark forests. More detailed maps may also differentiate farmers’ fields, barren tundra, deserts, prairie, ice sheets, and marshes. I have a full post on placing vegetation, but here I’ll give a quick summary:

Climate zones are critical to a region’s vegetation, and the biggest predictor for climate is latitude.* Any terrestrial planet will have bands of wet and dry. The climate tends to be wet near the equator and again in temperate regions.* Conversely, most land is dry about a third of the way to the poles* and dry* again at the poles themselves.

Mountains tend to be colder and wetter than their surroundings, and frequently one side of a mountain range will be wetter or milder than the other. If very different eco-regions don’t have mountains separating them, their transition will be gradual. For example, there’s rarely a cut-and-dry boundary between temperate forest and desert on flat ground. Instead there’s a gradual transition first to savannah, then grassland, then arid scrubland, and finally high desert.

Settlements

Humans (especially pre-industrial, agricultural humans) like to settle near rivers. All the earliest agricultural civilizations grew up along rivers.* Fresh, moving water provided something to drink, irrigation for crops, power for watermills* and highways for high-volume trade. In the ancient world, it was much easier to trade large quantities of goods via water than it was overland. This remained true until – well, until forever. It’s still true. Ocean coasts and rivers have tradeoffs: both offer good shipping routes, but rivers are sources of fresh water and fertile sediment while oceans are superior for fishing and whaling. Cities that become large and prosperous require not only water and resources but also trade.

Humans also construct some fortifications or settlements in defensible positions, such as atop hills and cliffs or on islands. But these structures will still be close to their centers of civilization (river valleys and coastlines), especially at first. Some fortresses may be found guarding remote mountain passes as well, once agricultural city-states grow into large nations.

Different humanoids – and different human cultures – could find different regions attractive for settlement. In high-stereotype fantasy, dwarves prefer underground or mountainous areas and elves prefer great forests.* Drow and sun-sensitive orcs, goblins, or trolls may require underground dwellings. But access to the lands above may be essential for resources or ventilation, necessitating karst landscapes rich with caves. Even garden-variety humans can grow large cities in nontraditional areas. This is especially possible once modern technology, magic, or domesticating a new herd animal makes it viable. For example, in North America we see cities in barren inland regions* due to modern technologies such as air conditioning; plus, highways and railways have become more important trade routes than rivers.

On Your Map:

Put most of your cities on rivers and/or coastlines unless you have a story-relevant reason not to. Don’t completely disregard this in science fiction, either. We humans might not be so reliant on rivers as we once were, but we still like them. The biggest cities tend to show up where trade routes intersect – at branches in rivers or on the coastline near an important mountain pass.

Roads

Roads must connect important centers of habitation and trade, and they also follow some of the same rules as rivers – if not so strictly. Roads will often track a river or coastline, because these are easy places to build roads* and most people will be living there anyway. Unlike rivers and coastlines, roads do occasionally need to pass over mountains. Humans will find the lowest and easiest possible routes through mountain ranges, and these routes will be important choke points for defense.

On Your Map:

If you choose to include roads, make sure you keep their style visually distinct from rivers, since they’ll be drawn alongside each other quite a lot. Otherwise, just play connect-the-dots with cities, and make roads sparser and more squiggly over hills or mountains.

Boundaries

Political boundaries are a special case. For starters, they’re drawn only onto maps and rarely marked on the face of the world itself. Boundaries have more in common with abstract human creations like “justice” and “sin” than with concrete* creations such as roads and towers. Yet they do follow certain rules, just like natural features and the less abstract trappings of civilization.

Boundaries often follow obvious natural barriers like mountains and rivers. But river boundaries have a different flavor than boundaries marked by a high mountain range, empty desert, or large lake. Though a river marks an arbitrary line that a boundary can follow, by default an agricultural civilization will fill up as much of a river valley as it can. Thus a boundary along a river is an “artificial” divide, likely separating two halves of the same culture. Rivers are common places for imperial conquerors to divide land, but they are almost never natural cultural boundaries. Not to mention, rivers on flat ground shift over time – so they can be unreliable for demarcation.

Boundaries that evolve naturally between two nations are more commonly mountains*, arbitrary lines in uninhabited deserts, choke-points on peninsulas, or wide bodies of water such as lakes or sea channels. Nations don’t always align perfectly to regions divided by these features – but there’s a good correlation. This correlation is strongest where the nations evolved naturally and weren’t given arbitrarily-drawn boundaries by imperial powers carving up the world.

On Your Map:

Before placing boundaries, ask yourself whether the boundaries were placed by locals or by external empires.

If these boundaries arose naturally between the local inhabitants, force your boundaries into uninhabited or difficult-to-traverse regions. If boundaries have been imposed by outsiders* at some point in history,* rivers and arbitrary straight lines should be more common.

Behold: The Realm of Badmap!

Getting a feel for how maps should look can take time, especially since there are so few hard-and-fast rules.* That’s where analyzing other maps – both real and fictional – can help. Most maps are pretty reasonable affairs; it’s rare to find one so ridiculously ill-conceived that it can illustrate all the “don’ts” of mapmaking in one place.

And so I’ve made that exact thing for your viewing displeasure! Can you point out all the very bad, not good features on the following map of the Realm of Badmap?*

I haven’t included boundaries or roads (they’re not always needed), but everything else is there. I’ve used the amazing Sketchy Cartography Brushes by Deviant Art’s StarRaven, which I highly recommend. I apologize for exploiting the brushes for this work of cartography evil. It had to be done. For, uh… for Science.

A Reasonable Map

Here’s a variant on the same general landmass but with reasonable features. I’ve tried to be as consistent as possible with the art style so that the only major differences are geological and climatological.*

This map still isn’t “perfect” because there is no singular perfect; the permutations of acceptable are vast. In fact, it’s statistically likely for a map of any given region to be not perfect. Even on Earth, curious “un-Earth-like” features do occur here and there. So for detailed continent-sized maps, I advise consciously adding an odd feature or two. The map I drew has some borderline-believable features. The big southern river exits to the coast through a mountain range.* The barrier islands are a bit far from the coastline in the northwest. And the vegetation patterns could suggest a reversed (compared to Earth) rotation of the planet.*

Be prepared to explain the existence of any anomaly on your map. Semi-plausible oddities can add interest to your world’s geological history or aesthetic, or cause some confusion among your world’s scholars. Why do those rivers seem to cross each other? Because of elaborate irrigation canals built by the Ancients making artificial under/over paths for the sacred streams. Why are there only foothills on one side of the mountain range? Because of the way the continent buckled to form them, or possibly the Earth God was just lazy that day.

But hopefully your maps will keep mostly to the plausible and believable, thanks in part to the guidelines and examples of this post. It would be a shame to craft a perfect story or game only to be mocked for your world’s impossible river or misplaced mountains.